102 THE NATURE AND ORIGIN OF LIFE 



relation to movement, is a little protoplasmic mass of vari- 

 able form enclosing foreign bodies within its own substance 

 in a vacuole containing water. Suppose the ingested body 

 to be a living body. Every living body has its own per- 

 sonal colloid or protoplasmic state, which is the condition 

 sine qua non of its life. In the present instance, therefore, 

 the physical equilibrium of the liquid in the vacuole has 

 to undergo two antagonistic strains from two different pro- 

 toplasms, of which one is enclosed within it while the other 

 surrounds it. One of the two wins the day ; the other dies 

 and is physically assimilated or digested by the first. Here 

 is a struggle between two protoplasmic activities through the 

 intermediary of an interposed liquid, the liquid of the vacu- 

 ole. When the amoeba carries the day, we say that the 

 vacuole, having filled itself with the 

 amoeba's digestive juices, has diges- 

 ted and assimilated the ingested 

 animal. 



We can narrate in the same way 

 the history of a bacteridium injected 

 FlG 4 into a sheep ; only here the interior 



medium of the sheep takes the place 



of the amoeba's vacuole. The thing is to know whether the 

 bacteridium will assimilate the sheep or the sheep assimilate 

 the bacteridium. But, once the struggle is over, it is plain 

 that the interior medium of the sheep will contain the 

 transportable activity which won the day. As we have 

 seen, this is the origin of serumtherapy. 



The same story may be told when the ingested or injected 

 body is a dead colloid. Such a colloid, inasmuch as it is a 

 definite colloid, owes its existence to its particular physical 

 state. The thing is to know whether the injected colloid 

 will win the day over the interior medium of the animal, on 



