THE BLOOD 113 



mostly by way of experiment, have shown 

 that in the blood there are substances which 

 are of physiological importance although their 

 quantities may be so small as to be beyond 

 our present methods of analysis. These 

 bodies seem to act as chemical defensive agents 

 against disease. It is well known that the leu- 

 cocytes act as phagocytes, that is they seize, 

 hold, and devour bacteria and other micro- 

 organisms. But, in addition to this phago- 

 cytic action of leucocytes, the fluid of the blood 

 contains substances that are bactericidal. 

 These substances, probably protein in their 

 character, are destroyed by heating the blood 

 for an hour to 55 C. Possibly they are 

 derived from leucocytes. They may be called 

 bacterio-lysins. Other substances in the blood 

 may have the power of destroying red cor- 

 puscles. Thus the blood serum of one animal 

 has the power of dissolving the red corpuscles 

 of another species. Such bodies are called 

 haemolysins. 



The importance of these bodies is now 

 generally recognized. Bacteria or bacilli of 

 many kinds, if they find entrance into the 



