64 



ESSENTIALS OF CHEMICAL PHYSIOLOGY 



useful as foods. Snake venom is an instance of a very virulent 

 poison of protein nature. 



There is another class of chemical transformations which at first 

 sight differ very considerably from all of these. They, however, 

 resemble these fermentations in the fact that they occur indepen- 

 dently of any apparent change in the agents that produce them. 

 The agents that produce them are not living organisms, but chemical 



FIG. 13. Typical forms of Schizomycetes (after Zopf) : a, micrococcus ; &, uiacrococcut; ; c, bac- 

 terium; d, bacillus; e, clostridium ; /, monas Okenii; y, leptothrix ; h, i, vibrio; *, spirillum; 

 /, spirulina ; m, spiromonas ; n, spiroclisete ; o, cladothrix. 



substances, the result of the activity of living cells. The change of 

 starch into sugar by the ptyalin of the saliva is an instance. 

 Ferments may therefore be divided into two classes : 



1. The organised ferments torulse, bacteria, &o. 



2. The unorganised ferments or enzymes like ptyalin. 



Each may be again subdivided according to the nature of the 

 chemical change produced. 



In digestion, the study of which we are just commencing, it is the 



