578 IMMUNITY 



serum is heated at 55° C, as has been shown by G. Dean and 

 others ; and Muir and Martin have shown that this thermostable 

 immune-opsonin (bacteriotropin of Neufeld) has all the specific 

 characters of anti-substances in general. -On the other hand, 

 they have found that the thermolabile opsonin of a normal 

 serum has quite different properties. For example, when a normal 

 serum is tested on a particular bacterium, the opsonic effect on 

 that bacterium may be removed by treating the serum with 

 other bacteria ; in other words, the thermolabile opsonin of 

 normal serum does not possess the specific character of the 

 opsonin developed in the process of immunisation. They have 

 also found that various substances or combinations of substances 

 which act as " complement absorbers " also remove the opsonic 

 property from a normal serum, while they have no effect on an 

 immune-opsonin. 



That this thermolabile normal opsonin can act in a non- 

 specific way is shown by the fact that particles of car- 

 mine and other substances become opsonised by the action 

 . of normal serum. It is, however, to be noted that in certain 

 cases there have been found in a normal serum traces of sub- 

 stances which can be activated by thermolabile opsonin after 

 the manner of immune-body and complement (as seen in the 

 hemolytic action of a normal serum, p. 576) ; to this extent the 

 opsonic effect of a normal serum may have some degree of 

 specificity. From this and other facts some observers have 

 attempted .to explain the whole of opsonic action according to 

 the scheme of immune-body + complement as seen in haemo- 

 lysis. This, however, is not justifiable, since normal thermo- 

 labile opsonin can, as we have seen, act by itself, as can also 

 the specific immune-opsonin after normal opsonin has been 

 destroyed by heating ; and we know of no corresponding action in 

 the case of an immune-body. The subject is one of considerable 

 complexity, but it may be said that the most important varia- 

 tions in the opsonic content observed in infections depend on 

 the specific immune-opsonins, though the presence of immune- 

 body may play a part in raising the index, by leading to the 

 union of more normal-complement-opsonin. 



(c) Agglutination. — Charrin and Roger in 1889 observed 

 that when the bacillus pyocyaneus was grown in the serum of 

 an animal immunised against this organism, the growth formed 

 a deposit at the foot of the vessel ; whereas a growth in normal 

 serum produced a uniform turbidity. Griiber and Durham, in 

 investigating Pfeiffer's reaction, found that when a small quantity 

 of an anti-serum is added to an emulsion of the corresponding 



