Part 1

Transcriber’s notes:

In this transcription, paired _underscores_ denote _italicised text_. A single underscore preceding curly brackets indicates that the bracketed character is subscripted (mostly in chemical formulae, e.g. CO_{2}). Footnotes have been positioned below the relevant paragraphs.

Punctuation inconsistencies have been corrected silently, except for those occurring in footnote reference sources, which remain as in the original.

Inconsistencies of hyphenation, use of italics, and spacing of abbreviations (such as i.e. and c.c.) have not been changed.

In a large table following page 31, apparent inconsistencies of the authors of referenced sources are as in the original. Some of the figures in this table are indistinct.

Passages of German text contain possible typographic errors that have been left as in the original.

Spelling inconsistencies have not been altered, e.g. albumin/ albumen/albumine/albumid, but the following overt spelling errors were corrected:

synonomous —> synonymous an Medndel —> and Mendel akaline —> alkaline Wochenscrift —> Wochenschrift by —> bei transferrence —> transference quantitity —> quantity recticulin —> reticulin sythetical —> synthetical Elaatin —> Elastin hiaton —> histon

CARTWRIGHT LECTURES

1894

ON

DIGESTIVE PROTEOLYSIS

BEING THE CARTWRIGHT LECTURES

FOR 1894

DELIVERED BEFORE THE ALUMNI ASSOCIATION OF THE COLLEGE OF PHYSICIANS AND SURGEONS OF NEW YORK.

BY

R. H. CHITTENDEN, Ph.D.

_Professor of Physiological Chemistry in Yale University_

NEW HAVEN, CONN.: TUTTLE, MOREHOUSE & TAYLOR, PUBLISHERS. 1895

THE TUTTLE, MOREHOUSE & TAYLOR PRESS, NEW HAVEN, CONN.

PREFACE

The present volume, as explained by the title, consists mainly of a reprint of the Cartwright Lectures for 1894. These lectures were originally printed in the current numbers of the Medical Record, but so many requests have been made for their publication in a more convenient and accessible form that they are now re-issued, through the courtesy of the publishers of the Record, in book-form.

It is hoped that these lectures may prove of value not only in calling attention to some of the fundamental chemico-physiological facts of digestion, but in stimulating closer investigation of the many questions which are so intimately associated with a proper understanding of the processes concerned in the digestion and utilization of the proteid food-stuffs.

R. H. CHITTENDEN.

CONTENTS.

LECTURE I.

_The general nature of Proteolytic Enzymes and of Proteids._

Introductory observations, 1

Early history of gastric digestion, 3

The proteolytic power of the pancreatic juice, 7

The general nature of proteolytic enzymes, 8

Origin of proteolytic enzymes, 8

Preparation of pepsin, 10

Reactions and composition of proteolytic enzymes, 13

The proteid nature of enzymes, 15

Conditions modifying the action of enzymes, 17

The influence of temperature on proteolytic action, 18

The influence of acids, alkalies, and other substances on the activity of enzymes, 20

Action of chloroform on pepsin, 21

Theories of enzyme action with special reference to catalysis, 22

The general nature of Proteids, 27

Classification of proteids, 29

Chemical composition of some of the more prominent proteids occurring in nature, 31

Chemical constitution of proteids, 33

The presence of hemi- and anti-groups in all typical proteids, 34

Cleavage of the albumin-molecule with dilute sulphuric acid, 34

Hydration and cleavage of albumin by the action of superheated water, with formation of atmid-albumoses, etc., 37

Action of powerful hydrolytic agents on proteid matter, 39

Initial action of pepsin-acid on proteids, 40

Scheme of the general line of proteolysis as it occurs in pepsin-digestion, with a view to the structure of the albumin-molecule, 41

LECTURE II.

_Proteolysis by pepsin-hydrochloric acid, with a consideration of the general nature of proteoses and peptones._

Proteolysis by pepsin-acid, 44

Formation of hydrochloric acid in the gastric glands, 45

Liebermann’s theory regarding the formation of the acid of the gastric juice, 46

Differences in the action of free and combined acid, 47

Proteolysis in the presence of combined acid, 49

The combining power of various forms of proteid matter with hydrochloric acid, 51

Quantitative estimation of the affinity of the products of digestion for acid, 53

Richet’s theory regarding the conjugate character of the acid of the gastric juice, 54

Proteolysis in the presence of amido-acids, 55

Necessity for knowing the amount of combined acid in the stomach-contents, 57

Antiseptic action of the hydrochloric acid of the gastric juice, 58

The maximum action of pepsin exerted only in the presence of free hydrochloric acid, 59

Division of the products of pepsin-proteolysis into three main groups, 60

Detection of the products of digestion, 61

Separation of proteoses and peptones from a digestive mixture or from the stomach-contents, 62

Some of the chemical properties of peptones, 64

The so-called propeptone a mixture of proteoses, 65

Pepsin-proteolysis synonymous with a series of progressive hydrolytic changes, 66

Chemical composition of proteoses and peptones, 67

Pepsin-proteolysis a true hydrolytic and cleavage process, 71

Schützenberger’s results on the formation of fibrin-peptone, 72

Amphopeptones the final products of gastric digestion, but proteolysis never results in complete peptonization, 73

Solution of a proteid by pepsin-acid not synonymous with peptonization, 75

Influence of the removal of the products of digestion on the activity of the ferment, 75

Lack of complete peptonization by pepsin-acid not due to accumulation of the products of digestion, 76

The diffusibility of proteoses and peptones, 77

Absorption of peptones from the living stomach, 79

Differences between natural digestion in the stomach and artificial proteolysis, 80

Relative formation of proteoses and peptones in the living stomach, 81

Gastric digestion merely a preliminary step in proteolysis, 81

Intestinal digestion alone capable of accomplishing all that is necessary for the complete nourishment of an animal, 82

Some physiological properties of proteoses and peptones, 83

The experiments of Schmidt-Mülheim and Fano on the action of peptones when injected into the blood, 84

Physiological action of albumoses, 85

Introduction of albumoses into the blood, 87

Proteose-like nature of the poisons produced by bacteria, 89

The acrooalbumoses formed by the tubercle-bacillus, 90

Toxic nature of proteoses and peptones, 91

LECTURE III.

_Proteolysis by trypsin--Absorption of the main products of proteolysis._

Proteolysis by trypsin, 93

Comparison of pepsin and trypsin, 94

Trypsin especially a peptone-forming ferment, 95

The primary products of trypsin-proteolysis, 95

Scheme of trypsin-digestion, showing the relationship of the products formed, 96

The fate of hemi-groups in trypsin-proteolysis, 97

The primary products of trypsin-digestion mainly antibodies, 98

Character and composition of antipeptones, 99

Antialbumid as a product of pancreatic digestion, 100

The peculiar action of trypsin in the formation of amido-acids, etc., 101

Formation of lysin and lysatin in pancreatic digestion, 103

The relationship of lysatin to urea, 105

Formation of tryptophan or proteinochromogen by trypsin, 105

Appearance of ammonia in trypsin-proteolysis, 107

Relationship between artificial pancreatic digestion and proteolysis in the living intestine, 109

Leucin and tyrosin products of the natural pancreatic digestion in the intestine, 112

The physiological significance of leucin and tyrosin, 113

Absorption of the main products of proteolysis, 116

Absorption of acid-albumin, alkali-albuminate, etc. 117

Absorption limited mainly to the intestine, very little absorption from the stomach, 119

The change which the primary products of proteolysis undergo in the process of absorption, 120

Peptones not present in the circulating blood, 121

The change which peptones and proteoses undergo by contact with the living mucous membrane of the small intestine, 122

Retrogression of peptones by contact with other living cells, etc., 125

Functional activity of leucocytes in absorption, 128

Digestive leucocytosis incited by nuclein, 131

Shore’s experiments on the ability of lymph-cells to assimilate either proteoses or peptones, 133

Lymph a true secretion from the blood-vessels, 134

Direct excitatory effect of peptones when present in the blood on the endothelial cells, 136

Selective activity of endothelial cells, 137

DIGESTIVE PROTEOLYSIS

LECTURE I.

THE GENERAL NATURE OF PROTEOLYTIC ENZYMES AND OF PROTEIDS.

INTRODUCTORY.

In digestive proteolysis we have a branch of physiological study which of late years has made much progress. Chemistry has come to the aid of physiology and by the combined efforts of the two our knowledge of the digestive processes of the alimentary tract has been gradually broadened and deepened. That which at one time appeared simple has become complex, but increasing knowledge has brought not only recognition of existing complexity, but has enabled us, in part at least, to unravel it.

By digestive proteolysis is to be understood the transformation of the proteid food-stuffs into more or less soluble and diffusible products through the agency of the digestive juices, or more especially through the activity of the so-called proteolytic ferments or enzymes contained therein; changes which plainly have for their object a readier and more complete utilization of the proteid foods by the system.

In selecting this topic as the subject for this series of Cartwright Lectures I have been influenced especially by the opinion that both for the physiologist and the physician there are few processes going on in the animal body of greater importance than those classed under the head of digestion. Further, few processes are less understood than those concerned in this broad question of digestive proteolysis, especially those which relate specifically to the digestion of the various classes of proteid food-stuffs, and to the absorption and utilization of the several products formed. Moreover, the subject has ever had for me a strong attraction as presenting a field of investigation where chemical work can advantageously aid in the advance of sound physiological knowledge; and certainly every line of advance in our understanding of the normal processes of the body paves the way for a better and clearer comprehension of the pathological or abnormal processes to which the human body is subject.

You will pardon me if I specially emphasize in this connection the fact that advance along the present lines was not rapid until physiologists began to appreciate the importance of investigating the chemico-physiological problems of digestion by accurate chemical methods. Something more than simple test-tube study, or even experimental work on animals, is required in dealing with the changes which complex proteids undergo in gastric and pancreatic digestion. The nature and chemical composition of the proteids undergoing digestion, as well as of the resultant products, are necessary preliminaries to any rightful interpretation of the changes accompanying digestive proteolysis; but physiology has been slow to appreciate the significance of this fact, and, until recently, has done very little to remedy the noticeable lack of accurate knowledge regarding the composition and nature of the proteid and albuminoid substances which play such an important part in the life-history of the human organism, either as food or as vital constituents of the physiologically active and inactive tissues. This is to be greatly deprecated, since our understanding of the nature of proteolysis, of the mode of action of the enzymes or ferments involved, and of the relationships of the products formed, is dependent mainly upon an accurate determination of the exact changes in chemical composition which accompany each step in the proteolytic process. How otherwise can we hope to attain a proper appreciation of the real points of difference between bodies so closely related as those composing the large group of proteids and albuminoids? Surely, in no other way can we measure the nature or extent of the changes involved in the various phases of proteolysis than by a thorough study of chemical composition and constitution, as well as of chemical reactions and general properties.

In the early history of physiology there was, quite naturally, little or no thought given to the nature of proteolytic changes. The gastric juice, as one of the first digestive fluids to be studied, was recognized as a kind of universal solvent for all varieties of food-stuffs, and this even long before anything was known regarding its composition, but beyond this point knowledge did not extend. Active study of the gastric juice, as you well know, dates from 1783, when the brilliant Italian investigator Spallanzani commenced his work on digestion. The names of Carminati, Werner and Montégre[1] are also associated with various phases of work and speculation in this early history of the subject, especially those which pertained to the possible presence of acid in the stomach juices. In 1824, however, Prout showed conclusively that gastric juice was truly acid, and, moreover, that the acidity was due to the presence of free hydrochloric acid, and not to an organic acid. Still, many observations failed to show the presence of an acid fluid in the stomach, and it was not until Tiedemann and Gmelin’s[2] masterly researches were published that the cause of this discrepancy was made clear. It was then seen that the secretion of an acid gastric juice was dependent upon stimulation or irritation of the mucous membrane of the stomach, and that so long as the stomach was free from food or other matter capable of stimulating the mucosa, it contained very little fluid, and that neutral or very slightly acid in reaction. These early observers also recorded the fact that the amount or strength of acid increased with the outpouring of the secretion, incidental to natural or artificial stimulation, thus giving a hint of the now well-known fact that any and every secretion may show variations in composition incidental to the character and extent of the stimulation which calls it forth.

[1] See Berzelius’s Lehrbuch der Chemie, Band 9, p. 205, 4te Auflage, for an account of these early discoveries.

[2] Tiedemann und Gmelin: Die Verdauung nach Versuchen. Heidelberg und Leipzig. 1826.

The period between 1825 and 1833 was characterized especially by the presentation of the many results bearing on gastric digestion obtained by Dr. Beaumont on Alexis St. Martin, followed a little later, in 1842, by a long period of experimentation by many physiologists, as Blondlot,[3] Bassow,[4] Bardeleben,[5] Bernard,[6] Bidder and Schmidt,[7] and many others on methods of establishing gastric fistulæ on animals, by which many interesting results were accumulated regarding the physiology of gastric digestion. Up to 1834, however, there was no adequate explanation offered of the solvent power of the stomach juice; aside from the presence of hydrochloric acid, nothing could be discovered by the earlier chemists to account for the remarkable digestive action. Eberle,[8] however, attributed to the mucous membrane of the stomach a catalytic action, and claimed that it only needed the presence of a small piece of the stomach mucosa with weak hydrochloric acid for the manifestation of solvent or digestive power. It remained for Schwann,[9] to show the true explanation of this phenomenon, and although he was unable to make a complete separation of the active principle which he plainly believed existed, he gave to it the name of pepsin. Wassmann, Pappenheim,[10] Valentin, and later Elsässer,[11] all endeavored to obtain the substance in a pure form, and Wassmann,[12] in 1839, surely succeeded in obtaining a very active preparation of the ferment--one capable of exerting marked digestive action when mixed with a little dilute acid. Thus, a true understanding of the general nature of gastric juice was finally arrived at, and the cause of its digestive power was rightfully attributed to the presence of the ferment pepsin and the dilute acid. Further, the analysis of human gastric juice made by Berzelius,[13] in 1834, showed that the secretion contains very little solid matter (1.26 per cent.), thus calling attention to the fact that the digestive power of this fluid is out of all proportion to the amount of pepsin, or even to the amount of total solid matter present, and consequently paving the way for a general appreciation of the peculiar nature of the dominant body, _i.e._, the pepsin.

[3] Traité analytique de la Digestion. Paris, 1842.

[4] Bulletin de la Société des Naturalistes de Moscou, vol. 16. 1842.

[5] Archiv für physiol. Heilkunde, vol. 8. 1849.

[6] Lecons de Physiologie de la Digestion. Paris, 1867.

[7] Die Verdauungssäfte.

[8] Physiologie der Verdauung. Würzburg, 1834.

[9] Ueber das Wesen der Verdauungsprocesse. Müller’s Archiv, 1836, p. 90.

[10] Zur Kenntniss d. Verdanuung. Breslau, 1839.

[11] Magenerweichung der Säuglinge. Stuttgart und Tübingen, 1846.

[12] Lehmann’s Lehrbuch d. physiol. Chem., Band 2, p. 41, 2te Auflage.

[13] Lehrbuch der Chemie, Band 9, p. 209.

The original conception regarding the manner in which gastric juice exerts its solvent power on proteid foods was apparently limited to simple solution; chemical solution if you choose, brought about by catalytic action, but without any hint as to the possible nature of the soluble products formed. Mialhe,[14] however, recognized the fact that this transformation, by which insoluble and non-diffusible proteid matter was converted into a soluble and diffusible product, was a form of hydration, comparable to the change of insoluble starch into soluble sugar, and he named the hypothetical product albuminose. Mialhe’s study of the matter in 1846 was followed by Lehmann’s[15] investigation of the subject, and the coining of the word peptones as an appropriate name for the soluble products of gastric digestion. The peptones isolated by Lehmann were described as amorphous, tasteless substances, soluble in water in all proportions and insoluble in alcohol. They were likewise precipitated by tannic acid, mercuric chloride, and lead acetate, and were considered as weak acid bodies, having the power of combining with bases to form salts of a more or less indefinite character. Twelve years later, in 1858, Mulder[16] gave a more complete description of peptones, but his study of the subject failed to advance materially our knowledge of the broader questions regarding the nature of the process, or processes, by which the so-called peptones were formed. A year later, in 1859, Meissner[17] brought forward the first of his contributions, and during the following three or four years several communications were made representing the work of himself and pupils upon the question of gastric digestion, or more especially upon the character of the products resulting from the digestive action of pepsin-hydrochloric acid.

[14] Canstatt’s Jahresbericht d. Pharm., 1846, p. 163.

[15] Lehmann’s Physiologische Chemie, Band 2, p. 318.

[16] Archiv f. d. Holländ. Beitr., 2, 1858.

[17] Zeitschr. f. rat. Med., Band 7, 8, 10 und 14.

The general tenor of Meissner’s results is shown in the description of a row of products as characteristic of the proteolytic action of pepsin-acid on proteid matter. In other words, there was a clear recognition of the fact that proteid digestion in the stomach, through the agency of the ferment pepsin, is something more than a simple conversion of the proteid into one or two soluble products. The several bodies then isolated were named parapeptone, metapeptone, dyspeptone, α, β, and γ peptone; names now seldom used, but significant as showing that at this early date there was a full appreciation of the fact that digestive proteolysis as accomplished by the ferment pepsin is an intricate process, accompanied by the formation of a series of products which vary more or less with the conditions under which the digestion is conducted.