Goodhart(4), employing this method, estimated at intervals of fifteen

Transcription

1 THE FACTORS INFLUENCING THE CONCENTRATION OF HYDROCHLORIC ACID DURING GASTRIC DIGESTION. BY HUGH MAcLEAN AND WILLIAM J. GRIFFITHS. (From the Medical Unit Laboratories, St Thomas's Hospital.) IN recent years a very important part has been attributed to the regurgitation of alkaline intestinal contents into the stomach during digestion. That some regurgitation does occasionally take place is certain, but evidence is brought forward in this paper which shows that any regurgitation which may occur plays but a very insignificant part in the physiology of digestion. The presence of bile in the contents of the stomach has often been observed. It has perhaps been most frequently noted in vomited matter in which it sometimes occurs in large amount, but it is by no means rare to find it in specimens obtained from the stomach by means of a tube. Little, however, was known with regard to the significance of bile in the stomach until Boldyrev(1) undertook an investigation of this question. He confirmed an earlier observation by Pavlov that the introduction of oil into the stomach gave rise to a regurgitation of bile from the intestine; he also found that the introduction of mineral acids into the resting stomach provoked a regurgitation of alkaline duodenal fluid which reduced the acidity to a level (0.15 to 0-20 p.c.) at which it was acceptable to the intestine. Boldyrev's work was in general supported by Cathcart (2) and later by Carlson(3) and other observers. Before the publication of B oldyrev's experiments the regurgitation of intestinal contents into the stomach was regarded more or less as a pathological phenomenon, but the work of this observer seemed to give it a definite and important place in the chain of events occurring during gastric digestion, and led to the view that the concentration of hydrochloric acid in the stomach was controlled by this mechanism. After the introduction of the fractional method of gastric analysis by Rehfuss many observations were made bearing on this conception, and, on the whole, Boldyrev's conclusions were sustained. Bolton and Goodhart(4), employing this method, estimated at intervals of fifteen

2 64 H. MAcLEAN AND W. J. GRIFFITHS. minutes hydrochloric acid as well as total chloride and neutral chloride. They found, in common with other observers, that the hydrochloric acid rose to a certain height during digestion and then fell, the steepness of both rise and fall and the height of the curve being subject to considerable variations even in normal individuals. Fig. 1 shows a typical result obt *40_ 1P30 1P20 0 g i- I "- 100 S. D %X ~ 153 a 5 ~0.10/ Time in minites Fig. l. uve showing vaitions in hydrochloric acid, neutral chloride and total chloride after a test meal in a normal subject. tained by this method in a healthy person. The output of neutral chloride increased, somewhat less than the acidity, during the period in which the acidity was increasing, but when the acidity fell and as long as it continued to fall there was a marked rise in neutral chloride. Observations such as these were explained thus: at a certain point during digestion, when the curve of acidity was rising, the pylorus relaxred and allowed duodenal fluid to enter the stomach, thus reducing the acidity and correspondingly increasing the amount of sodium chloride. In various pathological conditions of the stomach these workers found

3 GASTRIC ACIDITY DURING DIGESTION. that there was a general relationship between the amount of neutral chloride and the concentration of acid; when the amount of acid remained high the neutral chloride remained low; when the neutral chloride was high the acid was comparatively low. They came to the conclusion that the general form of the curves obtained depended upon the amount of regurgitation, and was an index of the behaviour of the pyloric sphincter; at the present time this is the generally accepted theory. As the result of many investigations on the human subject it became apparent to us that this theory of regurgitation did not account for the facts, and that it was possible to place another interpretation on the curves described. In our experiments fractional test meals were used, consisting of a small amount of shredded wheat in about twenty ounces of distilled water. Before giving the meal the subject was asked to swallow a small stomach tube. By careful aspiration as much of the resting juice as possible was removed from the stomach. This is an important precaution. The meal was then given without removing the tube from the stomach. The subject was told not to swallow any saliva and was provided with a receptacle in which to collect it. As during the period of investigation some individuals secrete 150 c.c. or more of saliva, this is also important. Fractions consisting of about 10 c.c. were withdrawn at intervals by a syringe, delivered into special tubes, centrifuged and investigated as described below. In our experience, centrifugal separation is much preferable to filtration. In very many normal subjects, although no bile was detectable in the stomach, when the acidity of the contents fell the neutral chloride rose. Provided that we can suppose it possible for pancreatic fluid to enter the stomach unaccompanied by bile, this chloride might be supplied by the secretion of the pancreas, which as Carl Schmidt showed contains chloride up to 0 7 p.c. If pancreatic fluid does enter the stomach in any appreciable amount, the interaction of pancreatic alkali (sodium bicarbonate) with hydrochloric acid would lead to the liberation of carbon dioxide, and it should be possible to show its presence. In addition, proof of the presence of trypsin in the stomach would be valuable evidence in favour of regurgitation of pancreatic fluid. In what follows we describe experiments in which there was no obvious regurgitation, as indicated by the presence of bile in the fluid removed, but in which the gastric acidity followed the same course as when bile PH. LXV. 5 65

4 66 H. MaCLEAN AND W. J. GRIFFITHS. is found. In our experience the acidity curve has the same form in either case, whether bile is present or not. Estimation of C02 in fractional samples of gastric contents. If fluid containing bicarbonates should enter the stomach when this contains hydrochloric acid clearly carbonic acid would be liberated; collecting in the gas over the fluid contents this would raise the partial pressure of C02 in it, and consequently a larger amount would also be dissolved in the fluid, in simple proportion to this partial pressure so long as the fluid remained acid. But since equilibrium between the C02 in the fluid and in the gas over it would probably not be established instantly, if samples of the fluid could be removed soon enough after the reaction between bicarbonate and acid, quantities of C02 might be found in the fluid even larger than corresponded to this equilibrium. If the amount of bicarbonate was more than sufficient to react with all the hydrochloric acid then of coarse still larger amounts of C02 would be found in the fluid. Estimation of carbon dioxide under the conditions of the experiment proved to be a somewhat difficult problem. When sucked up by a syringe in the ordinary way the gastric fluid is subjected to a considerably reduced pressure, which favours the escape of C02 from the fluid. A method had to be devised whereby it was possible to ensure that any gas which escaped in this manner was collected and estimated. In addition, the gastric fluid had to be preserved from exposure to the atmosphere. Description of apparatus. The apparatus which was accordingly employed is shown in Fig. 2. A is the syringe and B the stomach tube. C is a centrifuge tube which fits on to a band of rubber on D. E is a small reservoir of paraffin. F contains about 10 c.c. of 40 p.c. caustic soda. G is an ordinary Bunsen valve placed so as to prevent any liquid from passing back from tube H, which contains 5 c.c. of N/2 sodium hydroxide covered by a layer of paraffin. Before carrying out an experiment a number of clean dry tubes were taken and into each was delivered 5 c.c. of N/2 sodium hydroxide, the surface of the liquid being immediately covered by a thin layer of paraffin. When preparing to remove a sample from the stomach a centrifuge tube was attached to D, I was closed, and J turned to communicate with F. By withdrawing the plunger of the syringe pure air was sucked into the apparatus and afterwards expelled by turning J to communicate with D. This operation was repeated once or twice to displace the air in the apparatus with C02-free air. Tube H, containing the measured amount of sodium hydroxide, was then attached. The stomach tube was then connected with the apparatus and, with J closed and I opened, sufficient gastric fluid was drawn into the syringe. Tap I was now closed again and J turned to communicate with C, when the fluid was gently expelled from the syringe into C. J was reversed, the syringe filled with air from F, J again reversed and the air driven through the apparatus, removing at the same time any fluid remaining in the tubing between A and C. A little paraffin was allowed to run from E on to the surface of the fluid in C so as to cover it completely. The apparatus was then swept through with pure air once or twice in the manner

5 GASTRIC ACIDITY DURING DIGESTION. 67 described above. Since all the air passes through the sodium hydroxide in H any carbon dioxide which escaped from the fluid then in C was trapped. For the next fraction the tubes C and H were changed and the operations repeated. Fig. 2. Apparatus for obtaining samples of gastric fluid without loss of C02. As it was necessary to know the volume of fluid removed, graduated centrifuge tubes were used, or the level was marked on the tube and the volume determined subsequently. The amount of carbon dioxide in the gastric fluid and in the N12 sodium hydroxide in H was determined by the method of Van Slyke(5). Generally 2 c.c of the fluid (gastric fluid or NaOH) were introduced into the apparatus and washed in with two portions of 0-5 c.c. of water. To ensure complete acidity, 2 c.c. of 2 N hydrochloric acid were added before extraction. After extraction, the volume of gas was recorded; the carbon dioxide was absorbed by 05 c.c. of N/2 sodium hydroxide and the volume of air remaining read off; the difference between these readings is the amount of carbon dioxide. The precautions necessary when carrying out such work were strictly observed. Pipettes were not blown into, and when dealing with sodium hydroxide we found it advisable to coat the outer surface of the ends of pipettes with a thin film of vaseline to reduce the amount of alkali Jeft adhering and exposed to the atmosphere. Since the /V/2 sodium hydroxide used invariably contained traces of carbonate, a blank determination was carried out and the necessary correction applied to the results. For each sample of gastric contents removed two results were obtained: (1) the total carbon dioxide in the 5 c.c. of sodium hydroxide, (2) the concentration of carbon dioxide in the fluid itself. The carbon dioxide represented by (1) is derived from the volume of gastric fluid removed; this volume being known, the percentage of carbon dioxide was calculated and added to (2). 5-2

6 68 H. MACLEAN AND W. J. GRIFFITHS. The C02 in thefluidfrom the stomach. Preliminary experiments were carried out in order to determine the effect of introducing sodium bicarbonate into the stomach during gastric activity. Forty minutes after taking a test meal and with the tube in the stomach 0'2 grm. of sodium bicarbonate in 5 c.c. of water was taken and washed down with a small quantity of water. In a sample obtained five minutes afterwards there was an increase in the amount of carbon dioxide from 2 c.c. to 32 c.c. per 100 c.c. gastric contents, and the amount of neutral chloride increased. On another occasion 0 05 grm. of sodium bicarbonate in 4 c.c. of water was swallowed at intervals, sometimes before, sometimes after removing a sample from the stomach. It will be seen (Table I) that even this small amount of alkali (equivalent to 6 c.c. of N/10 sodium bicarbonate) is capable of producing a marked increase in dissolved carbon dioxide. TABLE I. Showing effect of ingested bicarbonate on C02 of gastric contents. Time in minutes after C02 in c.c. taking Total Cl' Neutral Cl' per 100 c.c. meal Bicarbonate given N/10 N/10 HCI N/lO fluid grm. NaHCO grm. NaHCO grm. NaHCO ' *05 grm. NaHCO * X Having thus determined the possibility of detecting the entrance of small quantities of bicarbonate into the stomach, we proceeded to examine the gastric fluid after an ordinary test meal in many experiments on healthy subjects. We found that there was constantly a small amount of carbon dioxide dissolved in the gastric fluid averaging ffom 3 to 10 c.c. per 100 c.c. of fluid. Such variations as occurred were small, and bore no relation whatever to the curves of acidity and neutral chlorides. In a few cases, at the end of the experiment when a fair amount of bile was present, the C02 of the contents increased, but we were always unable to obtain any evidence in favour of regurgitation of pancreatic fluid in the absence of bile either as an intermittent phenomenon or as one occurring at a definite point in gastric activity. Sometimes, indeed, the C02 content

7 GASTRIC ACIDITY DURING DIGESTION. 69 was higher when the hydrochloric acid was increasing rapidly, and considerably lower when neutral chloride was rising and acidity decreasing. Table II shows the results obtained in three normal subjects. TABLE II. Showing amount of CO2 obtained from fractional samples of gastric contents obtained from normal subjects. It CO. in Time in Total Neutral c.. Per 100 C.c. Exp. minutes Bile Cl' N/10 Cl' N/1O HEC N/10 fluid 1 15 Absent VP 0* *4 45,, ,, * ,, * ,, X6 120,, 1X260 1X Absent ,, * *638 0* , 1* *2 105,, * Present * Absent ,, * * Present 0X In Exps. 1 and 2 it will be seen that the amount of C02 in the gastric contents did not vary to any appreciable extent during the whole period of digestion. In both these subjects the hydrochloric acid reached a maximum in approximately one hour, and then gradually declined while the neutral chloride steadily rose. This marked decrease in hydrochloric acid caused no increase in dissolved carbon dioxide. In some other experiments the average amount of C02 found was considerably higher and more erratic, but it never became consistently higher during the decrease of HCI and the increase of neutral chloride. On the other hand the presence of bile in Exp. 2 coincided with a definite increase in C02 content, and whenever bile was present in considerable amount the C02 content of the gastric fluid increased. lthe tryptic activity of the gastric contents. Regurgitation of pancreatic secretion during digestion should result in the presence of trypsin in the stomach, which should increase during the later stages of gastric activity when the hydrochloric acid is decreasing, if this decrease is due to neutralisation by fluid from the intestine. We carried out a number of experiments with a view to determining whether any significant amount of trypsin is actually present in the gastric contents during digestion and

8 70 H. MACLEAN AND W. J. GRIFFITHS. more particularly during the period of falling acidity. Spencer, Meyer, Rehfuss and Hawk(6) examined specimens of gastric contents after different meals for trypsin at different stages of digestion. They found that a tryptic enzyme was almost constantly present in the fasting and digesting stomach, and that the activity of this enzyme varied inversely as the acid content, usually following the colour changes due to bile. Hydrochloric acid and sodium bicarbonate when introduced into the stomach by mouth provoked regurgitation of bile accompanied by trypsin. The relationship between tryptic activity and acidity in these experiments cannot be said to be very distinct, nor do they throw much light on the question of regurgitation in the absence of bile. E8timation of tryp8in. After various attempts to estimate small amounts of trypsin the following method was adopted. A quantity (1 to 2 c.c.) of the centrifuged gastric contents was measured into a test-tube graduated at 10 c.c. After adding one drop of methyl red, the fluid was made faintly alkaline with N/10 sodium hydroxide. The reaction was then adjusted to a faint pink by cautious addition of N/100 sulphuric acid. Five c.c. of casein solution were added and the volume made up to 10 c.c. with water. The contents of the tube were thoroughly mixed by shaking. Two dry test-tubes were taken and into each 4 c.c. of this mixture were delivered. One portion which served as a control was brought to the boiling point and cooled. Both tubes were heated for two hours at 400C. in a water bath. When incubation was complete the tubes were removed from the bath and to each was added 1-5 c.c. of 25 p.c. trichlor-acetic acid whereby the undigested protein was precipitated. The mixture was filtered through a Whatman No. 1 filter paper, the first few drops being refiltered if necessary. It is essential that the filtrate should be perfectly clear. The total nitrogen in 4 c.c. of this filtrate was determined by the method of Folin and Denis, N/100 acid and alkali being employed. The casein solution was prepared as follows: two grams of pure casein were dissolved in a boiling solution of 17 c.c. of N/10 sodium hydroxide in 180 c.c. of water. Solution was facilitated by first rubbing the casein into a thin cream with a little of the alkali. The solution was filtered hot and the opalescent filtrate made up to 200 c.c. with water. Bile prevents complete precipitation of the protein by trichlor-acetic acid, a colloidal solution being obtained which will not yield a clear filtrate. When bile is present the sample must be diluted five to ten times before proceeding with the estimation. The tryptic activity was given by the amount of nitrogen in the soluble products yielded by 1 c.c. of alkaline gastric fluid after incubation, measured as c.c. of N/IOO acid, allowance being made for the control.. When the original fluid was diluted before estimation the tryptic activity was assumed to be proportional to the dilution. The method proved to be a very delicate one and gave definite results with very small amounts of trypsin. Results. Table III shows the results obtained in various subjects. In the resting juice considerable amounts of trypsin were present as might be expected. During gastric activity in some subjects a definite amount of trypsin was found, but only when bile was present. In all others only indefinite traces of trypsin were found notwithstanding a marked rise in neutral chlorides from the beginning and a definite fall in acidity subsequently. No relationship between the variations in

9 GASTRIC ACIDITY DURING DIGESTION. 71 TABLE III. Showing tryptic activity of fractional samples of gastric contents. Exp. 1 was done on a subject suffering from alcoholic gastritis, the others on normal subjects. Total Neutral Trypsin Exp. Time Bile Cl' N/10 Cl' N/10 HCI N/10 units 1 Resting - 0* min ,, ,, ,, - 0*302 0*250 0* ,, * ,, - 0*668 0*643 0* Resting - _ min. - 0'371 0*255 0* ,, *438 0* ,, *634 0* ,, - 1* ' ,, * Resting min ,, *488 0* ,, - 0*892 0X '8 75,, ,, 1*210 0* ,, *100 0* Resting trace min ,, 0*376 0* ,, - 0X421 0X131 0*290-60,, *099 0* ,, *410 90,, - 0*996 0*614 0* ,, Resting min. - 0* ,, - 0*108 0* ,, *262 0' ,, - 0*489 0* ,, - 0* * ,, - 0* ,, *638 0* ,, - 0' * tryptic activity and the curves of acidity was found in any subject. These experiments show very clearly that, in the absence of bile, it is rare to find more than minimal amounts of trypsin in the stomach during digestion; often it is 4uite absent. On one occasion, however, we did obtain a sample of resting juice which had a fair tryptic activity although containing no bile. Associated with bile the tryptic activity was always found to be considerable. Experiments with a test meal containing acid. Further evidence on the question whether alkaline fluid from the intestine enters the stomach during digestion was sought in the following way. If in subjects who secrete no hydrochloric acid an acid solution is introduced into

10 72 H. MAcLEAN AND W. J. GRIFFITHS. the stomach, acid sodium sulphate for instance, together with a test meal, the entry of an alkaline fluid through the pylorus would change the ratio of acid sulphate to total sulphate, whereas dilution with gastric juice, free from acid, would lower the concentration both of acid and total sulphate without altering this ratio. The first experiment on these lines was carried out on a young female subject in whom a fractional test meal showed entire absence of hydrochloric acid, both free and combined, with a definite secretion of neutral chloride. A meal was given consisting of 370 c.c. of wheat-meal fluid together with 188 c.c. of sodium hydrogen sulphate solution prepared by adding 50 c.c. of normal NaOH to 100 c.c. of normal H2S04 and 50 c.c. of distilled water. This mixture is too acid and unpleasant to drink, so it was injected into the stomach through a tube. The acidity of samples from the stomach was determined by titration; total chloride, sulphate and trypsin were also determined in each fraction. During the first hour and a quarter the acidity was reduced to roughly one-half of its initial value. As however the concentration of sulphate also fell and the ratio of titratable acidity to total sulphate was not changed, the acidity must have been reduced not by neutralisation but by dilution. After little more than two hours the acidity was still further reduced with only a very slight change in the ratio of acid to total sulphate, not more than could be accounted for by the secretion of alkaline mucus in the samples. The resting juice of this patient contained much bile and trypsin, but fractions removed after a meal was taken showed a small and decreasing amount of trypsin probably derived from a small residue of resting juice left in the stomach. There was no evidence of an increase of trypsin such as would be likely to accompany regurgitation. The curve of neutral chloride closely resembled a normal curve. The next experiment of this nature was carried out on a man known to have had achlorhydria for some time previously. No organic lesion of the stomach was present. A fractional test meal revealed entire absence of both free and combined hydrochloric acid. The chloride secretion was, however, perfectly normal. A fair amount of trypsin was present in the resting juice, but in subsequent samples the amounts were quite insignificant. When this patient was given sodium hydrogen sulphate the acidity of the stomach contents, after a preliminary delay, fell rapidly until in one hour after taking the meal the fluid removed from the stomach was actually faintly alkaline. There was only a very slight change in the ratio of acid to total sulphate, but a marked fall in sulphate. Many other

11 GASTRIC ACIDITY DURING DIGESTION. 73 experiments carried out gave similar results and showed very clearly that, when mineral acid is introduced into the stomach, it is possible for the acidity to be reduced and the stomach emptied with no evidence whatever that neutralisation plays any appreciable part in the reduction of the acid. It is highly probable that the diluting fluid brings neutral chlorides into the stomach, but this point will be discussed later. Experiments with a test meal containing sodium sulphate. When sodium sulphate is dissolved in an ordinary wheat test meal in such an amount as to make the concentration of S04" about 0.1 normal (5 grm. "anhydrous" Na2SO4 in 560 c.c. fluid) and the fractions removed after the meal are examined quantitatively for sulphate, it is in general found that the concentration of sulphate shows a progressive decrease until in about one and a half hours it has entirely disappeared from the stomach. In connection with these experiments we discovered a relationship between the amount of sulphate and the concentration of chloride in the fractions. The sum of the equivalent concentrations of S04" and Cl' proved to be remarkably constant throughout the interval between the ingestion of the meal and complete evacuation of the stomach. The results of one of these experiments are given in Table IV. Here the initial concentration of sulphate in the meal was roughly 0 12 normal, from which it gradually fell until in one and a half hours nothing but traces of sulphate remained in the stomach. TABLE IV. Normal subject. Meal: Five grams of "anhydrous" Na2SO4 dissolved in 560 c.c. of wheat test meal. S04 = 1 16 N/10 =0-824 p.c. Na2S04. Note the constancy of the sum of SO4" and Cl' in the fluid removed. Total Neutral Na2SO4 (SO4)" (Cl)' (Cl)' HCl (SO4)" grmi. + (Cl)' Time Bile Mucus N/10 N/10 N/I0 NIIO 100 c.c. N/10 Resting juice: (13 c.c.) trace min ,, ,, X *25 60,, *267 1X23 75,, - - 1X030 0X ,, '26 105,, * ,, ,, ,, trace Average value= 1 19 The sum of the equivalent concentrations of SO," and Cl' had an average value throughout the experiment of 0-12 normal.

12 74 H. MACLEAN AND W. J. GRIFFITHS. A number of similar experiments were carried out on normal subjects, and the results were so constant as to satisfy us that this relationship is not a chance one, but depends upon a peculiar property of the gastric mechanism. If we suppose that regurgitation of duodenal contents does not occur, and that the dilution of the meal, as shown by the falling sulphate, is brought about mainly by a mixture with gastric juice, this secretion must be the medium by which chloride is brought into the stomach. If the stomach contains sulphate solution of about 011 normal strength (with no chloride) the only way in which chloride can be added to the stomach contents so as to keep the concentration of chloride plus sulphate at 0.11 normal is by means of a solution of 0.11 normal chloride. If any of the mixture escape from the stomach the sum would still remain constant. We, therefore, regard these experiments as evidence that the gastric secretion under normal conditions has always approximately the same concentration of Cl' equal in strength to about 0.11 normal. This value corresponds roughly with the amount of Cl' in the plasma ( normal). It was in general found that the acidity commenced to fall, or was already falling, at the time of disappearance of sulphate from the stomach. At this point the stomach was practically empty. In some experiments in which we used sulphuric acid instead of sodium sulphate similar results to those with sulphate were obtained. DISCUSSION. In this paper we have endeavoured to show that the fall in acidity which occurs towards the end of normal gastric activity cannot be explained adequately on the basis of duodenal regurgitation. This reduction in gastric acidity has been shown to occur without any evidence of the simultaneous appearance of trypsin and carbon dioxide, which one would expect if a reflux of duodenal fluid had taken place. When acid is introduced into the stomach and the acidity of the contents is found subsequently to fall (Hicks and Visher(7) and Crohn(s)) the evidence we have adduced leads us to the conclusion that the acidity of the fluid introduced is lowered by the secretion of a neutral fluid containing neutral chloride. We consider that a similar process occurs in the later stages of digestion when the concentration of acid diminishes. Apperly9 has described the gradual attainment of a definite Cl'

13 GASTRIC ACIDITY DURING DIGESTION. concentration by the gastric contents after a test meal; he calls this the "chloride point." Its value is equal approximately to the concentration of chloride in the blood plasma, and he has shown that the juice in the resting stomach has a similar value. Our results are in agreement with his findings; we believe that the gastric glands secret e at all times, whether active or quiescent, a fluid having a fixed concentration of chloride ion. Since sodium chloride is found in the stomach in the absence of duodenal regurgitation, it must be secreted by the gastric glands. Gamble and Ross (1o) have described how after ligature of the pylorus in dogs the stomach secretion contains large amounts of sodium chloride. Gamble and Mc Iv e r(1) proved that the same phenomenon can occur in rabbits and remark that "the entrance into the stomach of a large amount of fixed base, more than three-quarters of the equivalence of Cl' loss, constitutes a finding which is probably of important significance as regards the construction and function of gastric juice." Later the same workers (12) demonstrated, on cats with gastric pouches, that in the presence of a fairly constant value for Cl' quite large variations in fixed base could occur; these variations seemed to depend on the nature of the meal. Pavlov(l3) believed that the acidity of the gastric juice is constant, although he observed that the first portions of the juice secreted from a gastric pouch were often less acid than subsequent samples; he ascribed this to partial neutralisation of the juice by mucus on the wall of the resting stomach, an effect which passed off in a short time. On the other hand, Rosemann(14), in similar experiments, observed that the change occurred both at the beginning and the end of secretory activity, while the total chlorine concentration remained fairly constant, and Katsch(15) holds that one must accept a variation in the hydrochloric acid of the gastric juice. There is, therefore, already evidence that (1) the gastric glands can secrete sodium chloride, and (2) that the concentration of this salt undergoes change. Since, as we have shown, duodenal regurgitation is not the prime factor in the regulation of gastric acidity, we have put forward evidence for the view that the chloride ion brought to the glands by the blood as sodium chloride is secreted at a definite fixed concentration, part of it unchanged as sodium chloride and part changed into hydrochloric acid, and that the extent of this change governs the acidity of the secreted juice. Thus during the early stages of digestion, when the acidity of the gastric contents is rising, there is a marked change of sodium chloride into hydro- 75

14 76 H. MAcLEAN AND W. J. GRIFFITHS. chloric acid, so that the neutral chloride curve is low; but when the acidity reaches a certain value, which may be different in different subjects, the degree of transformation of sodium chloride diminishes until more or less all this salt is secreted unchanged. This brings about a fall in acidity and a corresponding rise in neutral chloride as shown by the gastric analysis curves. Finally, when the stomach is empty, the rate of secretion falls to the fasting level and the juice takes on the character of the resting secretion, which is only slightly acid. CONCLUSIONS. (1) The fall in concentration of hydrochloric acid and corresponding rise of sodium chloride in the stomach contents during digestion are not brought about by regurgitation of alkaline fluid from the duodenum, as is generally supposed; slight regurgitation of alkaline fluid into the stomach occasionally takes place, but this plays little or no part in the regulation of gastric acidity. (2) The normal stomach secretes the chloride ion in about the concentration in which it is present in the blood. Some of the Cl' is secreted as hydrochloric acid while the remainder is secreted as neutral chloride, the proportion of the two forms being different at different stages of digestion. REFERENCES. 1. Boldyrev. Pfiiuger's Archiv p Q. Journ. Expt. Physiol. 8. p , 2. Cathcart. This Journ. 42. p Carlson. Amer. Journ. Physiol. 37. p Ibid. 38. p Bolton and Goodhart. Lancet, March 4th, Van Slyke. Journ. Biol. Chem. 30. p Ibid. 58. p Spencer, Meyer, Rehfuss and Hawk. Amer. Journ. Physiol. 39. p Hicks and Visher. Amer. Journ. Physiol. 39. p Crohn. Amer. Journ. Med. Sci p Apperly. Med. Journ. Australia, June Gamble and Ross. Journ. Clin. Invest. 1. p Gamble and McIver. Ibid. 1. p Journ. Expt. Biol. and Med. 23. p Pavlov. The Work of the Digestive Glands. Trans. by W. H. Thompson, London. Griffin. 2nd edn. (1910.) 14. Rosemann. Pfluiger's Archiv Katsch. Munch. Med. Wochenschr. 71. p