NEW CONCEPTIONS IN SCIENCE 



into another, it is entirely rid alike of red cor- 

 puscles and white. Clearly the lymph, then, must 

 contain some chemical substance which protects the 

 inoculated animal. And the serum of the latter 

 may in turn confer immunity upon other animals. 

 How has this curious result been brought about? 



Incidentally it is to be noted that often the action 

 of the serum is not bactericidal ; the fungi continue 

 to thrive and multiply, although their harmful 

 powers seem destroyed. It appears here as if the 

 serum merely neutralized the poison the microbes 

 secrete. Moreover, a puzzling fact, disclosed by 

 Bordet, was that the benign powers of the serum 

 may be destroyed simply by heating, but that this 

 power was instantly recovered by the addition of 

 a small quantity of serum from an animal which 

 had never been inoculated. In other words, the 

 serum of a non-inoculated animal, itself powerless 

 to confer immunity, could still restore the im- 

 munizing power to serum in which that power had 

 just been destroyed. Slight wonder if, before such 

 baffling paradoxes as these, the heads of the in- 

 vestigators sometimes began to swim. Metchni- 

 koff still held to the main lines of his theory. In 

 his view it was always the devouring cells which 

 intervene, either directly or in a less obvious 

 fashion, as in the case of the serums. To speak 

 with more precision, for him the process of im- 



