HvEMOLYTIC AND OTHER SERA 575 



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 certain amount of evidence, or whether, as Bordet 

 holds, there is a single complement which may, however, show 

 slight variations in behaviour towards different immune-bodies. 

 There is at least no doubt that all the complement molecules in 

 a serum are not the same. For example, Muir and Browning 

 have shown that the treatment of a normal serum with a small 

 amount of emulsion of a bacterium will remove the bactericidal 

 action for another bacterium, whereas the amount of complement 

 as tested by haemolysis is practically unchanged. They accord- 

 ingly consider that there is a moiety of complement, " bacterio- 

 philic complement," which is specially concerned in bactericidal 

 action. On the other hand, many of the arguments adduced 

 by Ehrlich and his co-workers in favour of a multiplicity of 

 complements are open to another interpretation; the truth 

 probably lies between Ehrlich's and Bordet's views. 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. This cannot be held as 

 proved. On the contrary, there are facts which are strongly in 

 support of the view that complement exists in the free condition 

 in the circulating blood. There is, however, 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, comple- 

 ment and the homologue of an immune-body can be distinguished. For 

 example, guinea-pig's serum is hsemolytic to 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 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. Hsemolytic sera are of great 

 service in the study of the question of specificity. Each is specific in the 

 sense already explained (p. 558), 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 hsemolytic, but in many cases 

 when heated at 55 C. possesses also agglutinating and opsonic properties 

 towards the red corpuscles used. And further, it would appear that in 

 some cases at least the immune-body, hsemagglutimn, and hsemopsonin 



