PART II 



THE PROPERTIES OF AN ANTI-SERUM TO 

 A SERUM; DEVIATION OF COMPLE- 

 MENT AND ITS RELATIONS TO THE 

 PRECIPITIN TEST 



Recent researches on the subject of immunity, and 

 especially those dealing with haemolytic sera, have thrown 

 a flood of light on the complicated constitution of serum 

 and other fluids and have given us the means of attacking 

 problems which were, and still are, quite inaccessible to 

 ordinary chemical methods. As has been shown above, 

 when bacteria or the cells of another species of animal are 

 injected into an animal, there are developed immune-bodies 

 which in association with complement or alexine produce 

 the bactericidal or haemolytic effect. From the point of 

 view of chemical combination the all-important fact is that 

 certain molecules or receptors in bacteria, &c., give rise to 

 anti-substances which lead to the fixation or absorption of 

 complement. It has also been shown that in a normal serum 

 in addition to complement there are also present the homo- 

 logues both of receptors and of immune-bodies. Accordingly 

 when a serum of one animal is injected into another of 

 different species there is theoretically the possibility of the 

 development of three different kinds of anti-substances. 

 Anti-complements have received most attention hitherto, 

 as their action was the first to be recognized, but recently 

 their existence has been called in question, as will presently 

 be explained. The subject of anti-immune-bodies, pro- 



