5 i6 THE POPULAR SCIENCE MONTHLY. 



ing of at least two reactions, in the first of which the ferment forms 

 with the substance to be decomposed a compound which is split up in 

 the second with the regeneration of the ferment. This has not been 

 experimentally proved for the real ferments, but it explains these proc- 

 esses so simply and completely that its correctness can not be doubted. 



These processes of fermentation have an extraordinary distribution, 

 for not only do the individual living cells produce ferments, but also 

 those which form parts of complicated organisms. This is especially 

 the case with those cells which are often united in enormous quantities 

 to form a larger organ. I will recall the salivary gland, the peptic 

 gland, and the pancreas, whose secretions are exceedingly rich in fer- 

 ments. This is of the greatest importance for the economy of the 

 animal organism, since it permits a considerable performance with a 

 comparatively small expenditure of means. 



I wish to call attention to another important peculiarity of the 

 processes of fermentation that is, to their sensibility to foreign in- 

 fluences. Some will only take place in a completely neutral or slightly 

 alkaline solution, others only in a slightly acid solution ; they all pro- 

 gress most rapidly at a certain temperature, and even slight deviations 

 from the most favorable conditions are sufficient to sensibly retard the 

 action of a ferment or to completely arrest it. The pepsin of the gas- 

 tric juice acts exclusively in acid solution (best in hydrochloric acid) ; 

 hence, if the gastric juice contains no free acid or only an organic 

 acid, such as lactic acid, the pepsin will produce no effect on albumen, 

 or only in a slight degree. 



Although I have just described this sensibility as a peculiarity of 

 the process of fermentation, it is not to be inferred that it is noticed 

 here exclusively ; on the contrary, we find it in all chemical processes, 

 only in a less degree. How many reactions take place only at a given 

 temperature, or at a given degree of concentration ? Creatine, for in- 

 stance, when boiled with baryta-water, is partly decomposed into urea 

 and sarcosine, and partly into ammonia and methylhydantoin ; and it 

 is evident that the possibility of splitting up in different directions is 

 increased with the size of the molecule. In the organism a large num- 

 ber of bodies are present which have a very complicated structure, and 

 are therefore readily decomposed. They have an ephemeral existence 

 only, but are, nevertheless, of the greatest importance in the economy 

 of the whole. Most of them are unknown to us, but in some cases 

 they have been successfully isolated. I will only mention glycogen, 

 the discovery of which is several decades old, and the purple of the 

 retina, which has only lately been recognized. All such complicated 

 compounds, having a high molecular weight, are capable of furnishing 

 very different products of decomposition under slightly modified con- 

 ditions. If, therefore, the decompositions in the organism should 

 always take place in the same manner, the governing conditions must 

 be exceedingly constant. Every product of decomposition, which is 



