160 ANTI-BACTERIAL PROPERTIES OF SERUM 



to the co-operation of two substances, namely, immune- 

 bodies and complements. 



Further light is still required before we can say to which 

 of these two types the opsonic action conforms, or whether, 

 indeed, it is peculiar to a single class of substances. The 

 work of Bulloch and Atkin 1 tends to show that opsonins 

 are simple substances resembling agglutinins, though differ- 

 ing from them in being more labile, while the results obtained 

 by Leishman 2 and by Dean 3 with regard to immune serums 

 strongly suggest that more than one substance may be 

 concerned, one of which resembles an immune-body. So 

 far, however, as the serums of normal animals are concerned, 

 practically all observers are agreed that the opsonic sub- 

 stance is in most cases destroyed to a vanishing point by 

 heating at a temperature of 55 C. No doubt Dean has 

 shown by a special method that traces of opsonic substance 

 can still be demonstrated in a heated normal serum, but 

 the general fact is that just stated. 



In the present research we have endeavoured to obtain 

 an answer to a single definite question, namely, Are the 

 opsonins of normal serum capable of being taken up through 

 the medium of immune-bodies ? The term ' complement ' 

 may be applied to the labile bodies in the serum which are 

 taken up by the complex receptor + immune-body, without 

 reference to what may be the toxic result of such a com- 

 bination. Unlike what is seen in the specific combining 

 affinity of immune-body, agglutinin, &c., for the correspond- 

 ing receptor, the haptophore group of complement shows, 

 as pointed out above, a certain community in its com- 

 bining affinities. The most diverse combinations of immune- 

 bodies with their corresponding receptors will take up the 

 same complement ; also a bacterial receptor + immune-body 



1 Bulloch and Atkins, ibid, vol. Ixxiv, p. 379. 

 8 Leishman, Trans. Path. Soc., London, 1905. 

 3 Dean, Proc. Roy. Soc., London, vol. Ixxvi, p. 606. 



