METHODS 105 



However all this may be, we recognize one colloid by 

 its action on another colloid ; and most of the time we 

 can verify directly that colloids follow a determined order 

 according to the foreseen result of their struggles, one 

 against another. 



For example, the rennet of the calf's stomach curdles 

 milk (the rennet's victory imposing its own colloid state 

 on the milk) ; gastric juice digests meat (victory of the 

 gastric juice) ; and so on. 



In some cases the colloid used as a reagent is a living 

 animal ; tetanic toxin kills man by producing in him certain 

 characteristic lesions. We can even say there is no colloid 

 reagent as sensitive and exact as living beings. 



But all these colloids which we call diastases or toxins, 

 when compared with the colloids which they are capable 

 of conquering by imposing their own physical state, have 

 to be considered as foods in relation to the animals which 

 digest them. Rennet injected into a rabbit is assimilated 

 by the rabbit, which develops the function (Rabbit x 

 Rennet), and the result is to produce in the rabbit such 

 a modification that its serum will henceforth annihilate in 

 vitro the effect of rennet on milk. There are certain yeasts 

 that feed perfectly well on tetanic toxin. A colloid, there- 

 fore, cannot be taken absolutely either as a toxin, a diastase 

 or a food : it is diastase for certain colloids and food for 

 others. Finally, there are other colloids indifferent to each 

 other, that is, capable of existing together without recipro- 

 cal influence. 



All the facts which we have established since we began 

 studying living beings by the natural and genuinely biological 

 method of investigation prove what I asserted at the start. 

 While vital phenomena bestride the chemistry and physics 

 of colloids, they are most accessible on the colloid side. 



