S.ILIYA 



49 



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. 

 Snake venom is an instance of a very virulent poison of proteid 

 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 

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

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



.. 17. — Bacilhis anthracis, the agent that produces anthrax or splenic fever (Koch): A, bacilli, 

 mingleii with blood corpuscles from the blood of guinea-pig, some of the bacilli dividing ; B, the 

 same after three hours' culture in a drop of aqueous humour. They grow out into long leptothrix- 

 like filaments, which subsequently divide ap, and spores are developed in the segments. 



Ferments may therefore be divided into two classes : — 



1. The organised ferments — torulae, bacteria, &c. 



2. The unorganised ferments or enzymes — like ptyahn. 



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 

 unorganised ferments with the action of which we have chiefly to 

 deal. The unorganised ferments may be classified as follows : — 



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

 into sugars. Examples : ptyalin, diastase, amylopsin. 



