histidine); the existence of an anti-group is said by them to be present on account of this fact, and also an intermediate stage between protones and hexones is probable.

Gulewitsch finds that only p-diacetylamidophenol, among many other less complex chemical compounds, is acted upon by trypsin, with the formation of acetic acid. He cannot confirm Nencki and Blank, who stated that hippuric acid was decomposed, and considers that their trypsin contained the fat-splitting ferment of the pancreas.

Baldwin and Levene find that the diphtheria and tetanus toxines are digested by trypsin, and thus rendered inert; the activity of tuberculine is only destroyed by the prolonged action of trypsin.

According to Cohnheim, the passage of peptone through the intestinal wall depends on its further decomposition into simpler compounds caused by a ferment which he has termed erepsin; it acts rapidly on proteoses and peptones, producing ammonia, leucine, tyrosine, lysine, histidine, arginine; it acts feebly upon histones, and not upon proteids except caseinogen; protamines are, however, acted upon.

Matthews even suggests that the centrosome in the unfertilized eggs of Arbacia plays the part of a proteolytic enzyme, as he has observed localized areas of liquefaction in the protoplasm.

CHAPTER XIX.

PROTEOLYSIS BY FERMENTS OTHER THAN PEPSIN

AND TRYPSIN.

A PROTEOLYTIC ferment has been discovered by Babcock and Russell in the ripening of cheese, which they have named galactase. It has an action like trypsin, alkaline media being the best, but it is not identical with it, and it is found in the milk of all animals. Albumoses, peptones, amino-acids, and ammonia are formed, these nitrogen compounds being fairly evenly .divided. It readily decomposes hydrogen peroxide, and it liquefies gelatine. These results have been confirmed by von Freudenreich.

A phenomenon, first described by Salkowski and termed autodigestion, occurs in the organs after death; it is not due to putrefaction, as it takes place in the presence of chloroform and sodium fluoride. Biondi has confirmed Salkowski in his observations, and shows that the enzyme which produces this action is not trypsin, as considered by Neumeister, in the following way: (1) xanthine-like substances are formed which in tryptic digestion are present in a latent condition; (2) autodigestion is not inhibited by an acid medium; (3) tryptophane is not a product, whereas it occurs in tryptic digestions.

K

Magnus-Levy has obtained i-lactic acid, d-lactic acid, and succinic acid; also formic, acetic, and butyric acids, hydrogen, carbon dioxide, and hydrogen sulphide from livers which were subjected to autolysis; further, glycocoll was obtained by Jacoby in autodigestion of the liver.

In yeast there is also a proteolytic enzyme, as Hahn found that an appreciable quantity of gelatine was dissolved in twenty-four hours by it, and he thus confirms Will as regards its presence in yeast; in conjunction with Geret he has shown that the albumin in yeast extract is decomposed with the formation of tyrosine and leucine. These investigators have further shown that it can digest added albumin in addition to that in the extract, with the formation of the same products; hypoxanthine is also found, its amount increasing during the digestion. They have termed this enzyme endotrypsin, and it resembles pepsin in requiring an acid medium, and trypsin in the nature of its products. In addition to the above products, Kutscher has isolated histidine, arginine, lysine, aspartic acid, and a compound CgH6O1N4.

A similar ferment has also been found in Aspergillus niger and other fungi by Bourquelot and Hérissey; this enzyme of Aspergillus niger has been found by Malfitano to act upon gelatine, nucleo-proteids, globulins, and albuminates, but not on egg-albumin. Emmerling and Reiser have investigated the action of Bacillus fluorescens liquefaciens on gelatine. Twenty-five per cent. of the nitrogen was eliminated as ammonia; and methylamine, trimethylamine, choline, and betaïne were identified in the solution. Fibrin gave peptone, arginine, leucine and aspartic acid when acted upon by this micro-organism.

Peptonising bacteria are also found in milk which produce an enzyme very similar to trypsin; in the fermentation of casein aromatic acids are formed as well as peptone, leucine, and tyrosine; and cane sugar can be inverted, but not lactose (Kalischer).

Proteolytic enzymes are also probably the cause of bacteriolysis, the term used for their autodigestion.

The vegetable ferment bromelin was discovered by Marcano in 1891, and the products of its action have been examined by Chittenden and his pupils. Except for a small residue, fibrin is completely dissolved, and is converted into the various albumoses and peptones, and finally into amino-acids. The small residue is called antialbumid. The other albumins behave similarly.

Papain, the proteolytic enzyme of the papaw tree, was first investigated by Wurtz in 1879, who said it converted albumins into peptones and leucine. Then, in 1883 and 1884, Martin made a complete examination, and found a milk-curdling ferment as well as a proteolytic one in the juice of this tree. The products of the digestion of fibrin were a globulin-like body, peptone, leucine, and tyrosine, more of the former than of the latter being formed.

Vegetable proteids are converted in a similar way, a small anti-albumid residue being left. Halliburton states that no peptone is formed from vegetable albumins by this enzyme, the process stopping short at the proteoses.

Harlay considers it intermediate in power between pepsin and trypsin, and he has obtained the same chromogen by its use as he obtained with pepsin.

Chittenden, who made very complete observations,

states that the nitrogen in the albumoses produced by vegetable ferments is less than in those produced by trypsin.

Emmerling has quite recently published the results he has obtained by the digestion of fibrin with papain; the fibrin dissolved giving peptone, which, by prolonged action, was converted into tyrosine, arginine, glycocoll, alanine, leucine, aspartic acid, and phenylalanine. Mendel and Underhill find that papain can act in both alkaline and slightly acid media, giving products corresponding closely to those obtained with pepsin; leucine, tyrosine, and tryptophane do not occur if bacteria are excluded; bromelin, however, readily forms leucine, tyrosine, and tryptophane, even in acid media.

A proteolytic ferment is also contained in the germinating seeds of the Lupin and other plants; it acts upon conglutin, giving leucine and tyrosine, but not asparagine, which is not regarded by Schulze as a primary product of the decomposition of albumin; Bokorny has observed the same decomposition by malt enzymes.

A theory to account for the action of these enzymes, especially papain, was published by Wurtz in 1881; he has compared the process with that which takes place in the formation of ether from alcohol and sulphuric acid. In this process, ethylsulphuric acid is first formed; this is then acted upon by alcohol, giving ether and sulphuric acid; a small quantity of sulphuric acid can thus transform large quantities of alcohol into ether. The enzyme is supposed to have the property of combining with the albumin, forming a compound which is decomposed by a further quantity of albumin, thus: