258 Chapter IX 



immunised animals, increased in volume and became greatly swollen, 

 settled the question in favour of Gruber's theory. But the objection 

 formulated by Kraus and Seng 1 , on the one hand, and by Bordet, 

 on the other, dealt a severe blow to this view. As the serum em- 

 ployed by Roger was not deprived of its cytases (alexine), the 

 viscosity of the membrane of the fungus could not be attributed 

 to the agglutinin. When Bordet 2 demonstrated that the red blood 

 corpuscles, under the influence of the serums, undergo an agglutina- 

 tion as marked as that seen in bacteria, it enabled us to study this 

 phenomenon in the large red corpuscles of birds, in which no one 

 has ever been able to demonstrate any viscosity of the corpuscular 

 stroma. In a mixture of red corpuscles of bird and mammal, sub- 

 mitted to the action of a serum which agglutinates the former only, 

 the red corpuscles of the mammal never unite with those of the bird, 

 although this should undoubtedly take place if the membrane of the 

 agglutinated corpuscles had really become viscous. All the facts 

 collected up to the present are, therefore, in favour of Bordet's 

 physical theory in which an analogy between the phenomena of 

 agglutination and of coagulation is traced. 



The point that interests us more particularly in regard to aggluti- 

 nation is the relation of this phenomenon to immunity. We have 

 already given (Chapter VII) the arguments which render it impossible 

 for us to attribute to the agglutinative property of the fluids of the 

 body any rdle, however unimportant, in natural immunity against 

 [272] micro-organisms. We must now study the importance of this 

 property in the condition of acquired immunity, in which the agglu- 

 tination of micro-organisms by the fluids of the body is much more 

 frequent and active than in natural immunity. 



The first question to be settled is the following: Is the aggluti- 

 native property really constantly present in the fluids of vaccinated 

 animals ? The blood serum of animals that have acquired immunity 

 is unquestionably usually agglutinative as regards the corresponding 

 micro-organism. This agglutination may be more or less pronounced, 

 but it certainly exists in the great majority of cases. Nevertheless, 

 examples can be cited in which, in spite of the refractory condition 

 acquired as the result of immunisation, the serum exhibits not 

 a trace of agglutinative power. Having demonstrated that several 

 bacteria (Bacillus pyocyaneus, Diplococcus pneumoniae, Vibrio 



1 Wien. klin. Wchnschr., 1899, S. 1. 



2 Ann. de I'Insl. Pasteur, Paris, 1898, t. xu, p. 688. 



