i LIVING MATTEE 29 



Here the basic group (NH 2 ) of one molecule of glycine is 

 united with the acid group (COOH) of the second, with loss of a 

 molecule of water a true polymerisation. It is clear that by the 

 same process another molecule of glycine may be united with this 

 compound (dipeptide), thus making a tripeptide, and so on. If 

 we remember that all other amino-acids are capable like glycine 

 of similar combination between themselves and with the molecules 

 of other ammo-acids, it is evidently possible to obtain a very 

 numerous series of different and more or less highly complex 

 compounds. 



Fischer and his school have already succeeded in producing 

 synthetically some seventy similar compounds ; the most complex 

 is an octadecapepti.de, which consists of eighteen molecules of 

 ammo-acid united together in this manner. 



It is important to note that many of these polypeptides, 

 particularly the more complex, give the biuret reaction, which, as 

 we have said, is the most characteristic test of protein, and that 

 some of them are digested by pancreatic juice, which disintegrates 

 them into the amino-acid components, as is the case with natural 

 proteins. 



IX. Enzymes and ferments must further be included in the 

 protein group, and belong in all probability to the nucleoproteins, 

 or, according to others, the scleroproteins. These, being elabora- 

 tion products of the living cell, represent, according to the latest 

 view (Hofmeister, 1901), the chemical instruments by means of 

 which all chemical changes of the different substances which 

 form the material substratum of living matter take place. These 

 chemical changes result in the disintegration of the complex 

 molecule into simpler compounds (cleavage by analytical ferments), 

 either by rendering it suitable in form and quality for assimilation, 

 as in the case of the various digestive ferments of the alimentary 

 canal in animals, or by setting free the potential energy which is 

 manifested in the form of heat or movement. To this large class 

 of analytic ferments another class of ferments is opposed, whose 

 work consists not in the chemical cleavage of substances with 

 large molecules, but in synthetic processes, in which simple 

 molecules unite to form more complex molecules, as occurs in the 

 so-called anabolic phase of metabolism in living organisms. The 

 theoretical existence of these supposed synthetic ferments has so 

 far not received any decisive proof. We will therefore content 

 ourselves with a rapid survey of the class of analytic ferments, of 

 which much has been learnt by recent work. 



The fermentative processes of decomposition were, until recently, 

 divided into two great classes which were very distinct from one 

 another. In the one class were placed all the non-organised 

 ferments or enzymes, which were regarded as the elaboration pro- 

 ducts of the various secreting glands, capable of being isolated, 



