FERiMEXTS AND FIlKMEX lATION. 



r.\ n.WIl) l-KASER HARRIS, M.D., H.Sc. (Loud.), D.Sc. (Birmingham). 

 Lecturer on Physiology, the University, Biniiinghcjui. 



Many people would hardly be prepared for the state- 

 ment that the clotting of milk, the decomposition of 

 a dead body and the digesting of one's dinner are 

 all regarded by physiological chemists as three 

 different examples of the same process, namely 

 fermentation. Yet such is the case : a ferment clots 

 milk, a ferment disintegrates dead matter, and 

 ferments render our food-stuffs capable of absorption. 

 In a vast number of instances where it would have 

 been previously said that such and such an action 

 was " vital." we now say that it is due to a ferment : 

 the action is none the less vital, howe\'cr. because 

 we have discovered the messenger sent out bv the 

 living substance to do its bidding. 



Now, while it seems reasonable to speak of the 

 digestion of our food as a vital process, because it 

 goes on inside our li\ing bodies, there seems nothing 

 particularlv vital about the clotting of milk to make 

 cheese, or. still less, anything vital about the decom- 

 position of a dead body ; yet each of the specific 

 agents whose activity brings about the digestion, the 

 clotting and the disintegration are solely the 

 products of life alone. A ferment is something pro- 

 duced, as far as we at present know, only by li\ing 

 matter for the purpose of effecting certain definite 

 changes in certain substances with which it is to 

 come in contact. The substances thus undergoing 

 change need not necessarily remain within the organ 

 which produced the ferment. For instance, the 

 ferment pepsine of the gastric juice can digest a piece 

 of meat, or fish, or an egg, in a glass vessel kept 

 at the temperature of the blood. This was the 

 discovery of Reaumur (1752), and of Spallan^ani 

 (1777), both of whom obtained gastric juice from 

 birds, and showed that the juice was capable of 

 carrving on digestion outside the body, and that the 

 meat was not putrified in the process. A young 

 medical man, Stevens, of Edinburgh, also in 1777, 

 published experiments on gastric juice and its 

 activity outside the bod\. Up to the time of 

 Reaumur, digestion and putrefaction were believed 

 to be processes of exactly the same order chemically. 

 The digestion of meat in a glass vessel is as " vital " 

 as its digestion in the stomach, because as yet no 

 chemist has manufactured pepsine, an organic 

 substance which under certain physical conditions 

 carries out the precise chemical changes which we 

 call digestive. No organic chemist has as jet made 

 pepsine in the sense that he has made sugar, or urea, 

 or indigo — -all of which were at one time believed to 

 be able to be made onlv through the instrumentalitv 



of life itself. Pepsine \\,im ^o nametl in lS.i(jl)\' 

 Theodor Schwann. 



Now what is it that the ferment has done to the 

 meat whether in the body or in the glass vessel ? 

 It has, in the first place, altered its ph\'sical state, 

 for the insoluble meat is now a solution filterable 

 and translucent, and, secondly, it has transformed it 

 chemically, for it now consists of highly soluble 

 substances known as peptones: the flesh, or fish, or 

 egg has been " peptonised," made cajiable of absorp- 

 tion into the blood. 



Hut the ferment has done nothing to the meat 

 which the chemist could not have done without 

 pei)siiie, had he been given sufficient time. By 

 boiling the meat for long enough under high 

 pressure, and therefore at a high temperature, he 

 could in the end ha\e jieptonised, or hydrolysed, the 

 egg-albumen which was what the ferment did in 

 half-an-hour at blood heat, and under ordinarx' 

 atmospheric pressure. 



In a particular case it has been calculated that a 

 ferment effects as much in six hours at 40° C as 

 water at that temperature, without a ferment, would 

 effect in three years. 



A ferment, then, is a vital agent, although not a 

 \ital substance, which accelerates the velocity or 

 rate of change of some physico-chemical process. 

 Pepsine is something manufactured and secreted 

 by the cells of the gastric glands, and no other cells 

 can vicariously manufacture it. We may take it as 

 a type of ferment : it is one of the longest known 

 animal ferments and it can be obtained in a state of 

 comparative purity. To obtain it, the very best 

 method is to chill an animal's pure gastric juice to 

 0^ C, when a fine powdery precipitate falls, closeh' 

 associated with the hydrochloric acid of the juice.* 

 This powder ma}" be purified, and on being carefulh- 

 dried will retain its digestive power indefinitely. 

 The full history of the discovery of the various 

 ferments and their characteristics is virtually the 

 history of the establishing of the doctrine of Bio- 

 genesis, which is, that life always arises from a 

 pre-existent living being and ne\-er from non-living 

 material. 



Into this subject we must not at present digress: 

 but to understand the present views of fermentation 

 we should transport ourselves back to the time when 

 fermentation was regarded by the acutest thinkers as 

 a purely chemical or non-vital affair. The con- 

 troversy was about the cause of "fermentation" par 

 excellence, that is alcoholic fermentation, the changing 



This only free acid" in the htiniaii body was discovered to be a constituent of gastric juice by the 

 English doctor Prout in 1824. 



