H^EMOLYTIC AND OTHER SERA 481 



with several doses of immune-body and then repeatedly washed 

 in salt solution be mixed with untreated corpuscles and allowed 

 to remain for an hour, then sufficient immune-body will pass 

 from the former to the latter, so that all become lysed on 

 the addition of sufficient complement. The combination of 

 complement, on the other hand, is usually of very firm nature. 

 It has been a disputed point whether there are several distinct 

 complements in a normal serum with different relations to 

 different immune-bodies, for which Ehrlich and his co-workers 

 have brought forward a large amount of evidence, or whether, 

 as Bordet holds, there is a single complement which may, how- 

 ever, show slight variations in behaviour towards different 

 immune-bodies. There is at least no doubt that all the com- 

 plement molecules in a serum are not the same. Workers of 

 the French school also hold that complement does not exist 

 in the free condition in the blood, but is liberated from the 

 leucocytes when the blood is shed ; though this cannot be held 

 as proved, there is evidence that the amount of free complement 

 increases after the blood is shed and some time later gradually 

 diminishes. 



The haemolytic action of a normal serum can be shown in 

 many cases to be of the same nature as that of an immune- 

 serum, that is, complement and the homologue of an immune- 

 body can be distinguished. For example, the guinea-pig's serum 

 is haemolytic to the ox's corpuscles ; if a portion of serum be 

 heated at 55 C. the complement will be destroyed ; if another 

 portion be treated with ox's corpuscles at*0 C., the natural 

 immune-body will be removed and only complement will be left. 

 Neither portion is in itself hsemolytic, but this property becomes 

 manifest again when the two portions are mixed. Haemolytic 

 sera are of great service in the study of the question of specificity. 

 Each is specific in the sense already explained (p. 466), but the 

 serum developed against the corpuscles of an animal may have 

 some action on those of an allied species, that is, some receptors 

 are common to the two species. This fact can be readily shown 

 by the usual absorption tests, for example, in the case of an 

 anti-ox serum tested on sheep's corpuscles. A close analogy 

 holds to what has been established in the case of agglutinins. 

 It is further of great interest to note that by the injection of red 

 corpuscles into an animal its serum not only becomes haemolytic, 

 but in many cases when heated at 55 C. possesses also agglu- 

 tinating and opsonic properties towards the red corpuscles used. 

 And further, it would appear that in some cases at least the 

 immune-body, hsemagglutinin, and haemopsonin are distinct 

 31 



