INFECTION AND IMMUNITY. 581 



are assumed to be concerned ; the heating destroys the 

 "complement," and thereby checks the process; but 

 the subsequent addition of the normal serum supplies 

 fresh "complement," and at once restores the activity 

 of the hsemolyzing receptors. 



Eighth, if blood containing a haemolysin or a cytoly- 

 sin be repeatedly injected into an animal, anti-bodies 

 "antilysins" are formed, and the serum of the animal 

 has the power of robbing a ha3molytic serum of its 

 haemolyzing function if mixed with it in a test-tube. 



Ninth, if normal blood, containing complement, be 

 injected into the same or another species of animal, anti- 

 complement is formed, which has the property of inhib- 

 iting the action of the complement. 



Tenth, if emulsions of dead bacteria be injected into 

 animals, the leucocytes of that animal may gain in 

 power to take up and destroy living bacteria of the same 

 species, a result usually attributed to an increase in the 

 opsoniziug power of the blood. 



Eleventh, there exists in the blood a body to which 

 Wright has given the name "opsonin," which has the 

 function of so acting upon bacteria that they may be 

 taken up by phagocytes. This preparation of the bac- 

 teria by opsonin is regarded as a pre-requisite to pha- 

 gocytosis. 



The foregoing sketch affords but an imperfect idea of 

 the vast amount of labor that has been and continues to 

 be expended upon this many-sided, absorbing topic. 

 Of necessity many important contributions have been 

 omitted, but those noted will serve to illustrate the lines 

 along which the solution of the problem has been 

 approached. As a result of such investigations, our 



