through an intermediate soluble stage into myogen fibrin,

thus:

Paramyosinogen

→myosin fibrin

Myosinogen soluble myogen→ myogen fibrin

He thus confirms Halliburton, that two proteids enter into the formation of the clot, and he regards Halliburton's myoglobulin as part of the myosinogen which is not coagulated.

Stewart and Sollman have obtained the same results, but they regard Von Fürth's soluble myogen as part of the paramyosinogen. Both the proteids are converted into insoluble myosin, the myosinogen passing first into a modification similar or identical to paramyosinogen, thus:

Paramyosinogen

→ myosin

Myosinogen→ paramyosinogen → myosin

They confirm Halliburton also, that coagulation is accompanied by an increase of acidity.

Another case of coagulation is said by Camus and Gley to take place in the fluid of the vesiculæ seminales, which is somewhat viscid. If a drop of the liquid from the prostate gland of the same animal, guinea-pig, rat, or hedgehog, is added to the first liquid, coagulation sets in. This change is stated by the observers to be due to an enzyme which they have named vesiculase, on account of the fact that the property is lost when the prostatic liquid is heated to 70° C. for fifteen minutes. Beyond these observations nothing further is known of this transformation.

I

CHAPTER XVII.

CHANGES OCCURRING IN ALBUMINS AS THE RESULT OF THE ACTION OF PEPSIN.

By far the most important changes which albumins and allied substances undergo as the result of fermentation are those produced by the digestive ferments of the animal organism, pepsin and trypsin. In plants similar ferments, bromelin and papain, have been found, which resemble trypsin in their action very closely.

The change which takes place in the albumins is known as proteolysis, and it consists in a breaking up of the very complex albumin molecule into smaller ones, the size and constitution of some of which, especially those obtained from trypsin digestion, are known. Since some of these later changes are known to take place by hydrolysis, it is very probable that the complex molecule is broken up in a similar way; especially so as the same results can be obtained with mineral acids or superheated steam. The changes are thus quite comparable to those produced in the carbohydrates, smaller molecules being obtained at each stage; here, however, the end-products are very much more various, and consist chiefly of amino-acids.

In the animal organism, albumins taken as food are first acted upon by the gastric juice of the stomach, which contains pepsin; and it is therefore most convenient to describe the changes produced by this ferment before going on to those produced by trypsin.

Pepsin, in order to produce proteolytic changes, must always be accompanied by an acid; in the gastric juice hydrochloric acid is always present in about 0.2-0.5 per cent. In this connection, observations have of late years been made by Mayer, Hahn, and Wroblewsky in particular, upon which acids are the most favourable to peptic action; and it has been found that oxalic acid produces the most speedy solution of the albumin. Next in order comes hydrochloric acid, then nitric, phosphoric, tartaric, lactic, citric, malic, sarcolactic or d-lactic, sulphuric, and acetic acids, in the order mentioned. dilution of 0.01-0.5 per cent. was the most favourable; pepsin will not act in an alkaline solution, and even neutral salts retard its action.

A

Very many investigations have been made upon the products of the action of pepsin upon albumins, fibrin and egg-albumin especially. The earliest were those of Meissner and his pupils, in 1859-62, who obtained the following substances: parapeptone, metapeptone, dyspeptone, a-peptone, B-peptone, y-peptone. Brücke, who made a determination of the products about the same time, could, however, only obtain two products, which corresponded to parapeptone and y-peptone.

Kühne, some years later, studied the action both of pepsin and trypsin, and found that the only real difference was that trypsin produced a more complete hydrolysis.

He obtained, by using pepsin, albumose and peptone; this he called amphopeptone on account of the fact that trypsin only converts half the peptone further into aminoacids. He considered the albumin molecule to be split up into two halves, antialbumose and hemialbumose, and devised the following diagram to represent these changes:

antipeptone (+) hemipeptone (= ampho-trypsin

amino-acids

peptone)

Fränkel and Langstein have recently shown that Kühne's amphopeptone consists of two substances; (1) a peptone; (2) a substance identical with the carbohydrate complex of albumin-albamin.

Chittenden, Neumeister, and others have somewhat recently studied the products of pepsin digestion very carefully, and they have come to the following conclusions: fibrin or egg-albumin is converted firstly into syntonin, chiefly by the action of the acid, and then this is split up into two primary albumoses, which are called protoalbumose and heteroalbumose. Heteroalbumose,

on standing under water, or on drying, is converted into dysalbumose, which can be reconverted by acids into heteroalbumose. These two albumoses then give deuteroalbumose, and subsequently peptone. The diagram shows these results more plainly :

Some interesting conclusions from the results of molecular weight determinations of peptone and protoalbumose by Sabanejeff as given by Neumeister seem appropriate here. Peptone was found to possess a molecular weight of about 400, and protoalbumose of 2400; thus on decomposition six peptone molecules would be obtained from one protoalbumose. Taking the albumin molecule as 15,000, then albumin would give altogether 40, and heteroalbumose would give 34 molecules of peptone.

The other albumins, when subjected to pepsin digestion, give very similar products; these may be tabulated as follows:

Chittenden and Mendel, who have investigated the changes produced in this substance, find that there is a gradual falling off of carbon in the percentage composition of these substances formed in the digestion; they suppose