Acquired immunity against micro-organisms 265 



extracts of leucocytes were always found to be markedly less active 

 than the blood and the fluids of the exudations, Gengou was obliged 

 to come to the conclusion that the agglutinins cannot be regarded 

 as products of the cells of the animal body; this he sums up by 

 saying that "in the increase of the agglutinative power of its blood 

 the organism of the animal plays only a relatively passive part" 



(p. 337). 



I think that, in spite of the facts established by Gengou, his 

 conclusion can scarcely be regarded as final. The agglutinative 

 property, developing in the animal body, must be attributed to 

 some cellular influence, because we know that the prolonged sojourn 

 of micro-organisms in the animal fluids is incapable of conferring 

 on them this power. As Gengou's experiments did not permit him 

 to attribute the formation of agglutinin to any formed element, it 

 must be concluded that, although perfectly exact, they were insuffi- 

 cient to solve the problem. Geugou killed his animals at a stage when 

 their blood was already pretty strongly agglutinative. At this stage 

 the organs only possessed it to a much more feeble degree. Perhaps, 

 if he had examined his animals at an earlier stage, when the blood 

 possessed a much less marked agglutinative power, he might have 

 obtained a more powerful agglutination with an extract of the 

 organs. In my researches on the resorption of cells, I observed, on 

 several occasions, that the abdominal fluid of guinea-pigs which had [279] 

 received an injection of goose's blood became agglutinative before 

 the blood serum. Later, however, the blood exhibited a greater 

 agglutinative power than did the peritoneal fluid. If to this fact 

 we add the results of van Emden's experiments, we shall be tempted 

 to assign to the cells found in the peritoneal exudation and in the 

 lymphoid organs a share in the production of the agglutinin. This 

 question of the origin of the agglutinative power is, however, a very 

 difficult one, and it is impossible, in the imperfect state of our 

 knowledge, to express oneself in a more positive fashion. Fortu- 

 nately, according to the whole of our data on this phenomenon, 

 the part played by agglutination in immunity can only be very incon- 

 siderable, and we may be allowed to consider our general problem 

 without concerning ourselves over much about the origin of the 

 agglutinative property. 



Among the definite results obtained from the study of the agglu- 

 tinins, it may be specially pointed out that these substances can 

 in no way be identified with the fixatives. These latter were, for 



