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Read Ebook: On Digestive Proteolysis Being the Cartwright Lectures for 1894 by Chittenden R H Russell Henry
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Ebook has 409 lines and 46136 words, and 9 pages
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-M?lheim 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
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
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.
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 Mont?gre 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 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.
See Berzelius's Lehrbuch der Chemie, Band 9, p. 205, 4te Auflage, for an account of these early discoveries.
Tiedemann und Gmelin: Die Verdauung nach Versuchen. Heidelberg und Leipzig. 1826.
Trait? analytique de la Digestion. Paris, 1842.
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