92 THE NATURE AND ORIGIN OF LIFE 



The results thus obtained from purely chemical, non- 

 colloid substances are of little interest ; yet we know that 

 men accustom themselves to increasing doses of morphine 

 and that Mithridates reached a point where he swallowed 

 with impunity large quantities of different poisons. The 

 introduction of colloids taken from other living beings 

 for example, elements from other animals (milk, blood, 

 liver, etc.) or filtered microbe cultures (toxins, diastases) is 

 infinitely more instructive. 



As only one of the two antagonists in this case is 

 living, we occupy ourselves only with an animal that sur- 

 vives the injection. At the end of a certain time all the 

 injected colloid has disappeared, assimilated by the living 

 animal which uses it as a food. The animal, after assimi- 

 lating the colloid, has apparently undergone no modifica- 

 tion ; and we might think that it was all the same to 

 feed the animal this or that colloid, provided it did not 

 die. 



Nevertheless, when the injected colloid is what we call 

 a toxin or a venom, we observe a modification in the 

 animal into which it has been injected. The words toxin, 

 or venom, are expressions altogether relative ; if they apply 

 to the species of animal studied, it is for this reason the 

 injection of such substances, in sufficient quantity, sickens 

 or slays a normal individual of the species. Suppose the 

 animal does not die ; when cured it will be able to receive 

 a new injection of the same toxin or venom without sick- 

 ening again, at least not so much as before. Finally, 

 it may become refractory to the toxin or venom and 

 support very large doses without suffering from it. 



Here, again, there has been functional assimilation 

 the development of the organ defined by the function of 

 resistance to the venom or toxin. 



