406 THE CHEMICAL COMPOSITION OF THE BODY [CH. XXV. 



bacteria appear to be either alkaloidal (ptomaines) or proteid in nature. 

 The existence of poisonous proteids is a very remarkable thing, as no 

 chemical differences can be shown to exist between them and those 

 which are not poisonous, but which are useful as foods. The most 

 virulent poison in existence, namely snake poison, is a proteid of the 

 proteose class. 



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 inde- 

 pendently of any apparent change in the agents that produce 

 them. The agents that produce them are not living organisms, 

 but chemical substances, the result of the activity of living cells. 



- 



o o ^ 'oo C 







<p 





FIG. 343. Types of micro-organisms : a, micrococci arranged singly ; in twos, diplococci if all the 

 micrococci at a were grouped together they would be called staphylococci and in fours, sarcinae ; 

 6, micrococci in chains, streptococci ; c and d, bacilli of various kinds (one is represented with 

 a flagellum); e, various forms of spirilla ; /, spores, either free or in bacilli. 



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, etc. 



2. The unorganised ferments, or enzymes like ptyalin. 



The distinction between organised ferments and enzymes is, how- 

 ever, more apparent than real; for the micro-organisms exert their 

 action by enzymes which they secrete. This has long been known 

 in connection with the invertin of yeast, and for the enzyme 

 secreted by the micrococcus urese, which converts urea into ammonium 

 carbonate. In recent years Buchner, by crushing yeast cells, succeeded 

 in obtaining from them an enzyme which produces the alcoholic fer- 

 mentation, and there is no doubt that what is true for yeast is equally 

 true for all the organised ferments, and in several cases this has been 

 already proved experimentally. 



The unorganised ferments may be classified as follows : 

 (a) Amylolytic those which change amyloses (starch, glycogen) 

 into sugars. Examples : ptyalin, diastase, amylopsin. 



