STUDIES ON THE SERUM OF VACCINATED ANIMALS. 11 



and Werigo * in particular, have shown. We shall have occasion to 

 consider the taking up by phagocytes of cholera vibrios injected 

 intravenously. We have already noted the almost instantaneous 

 occurrence of this phenomenon. 



The intensity with which phagocytosis occurs in infected animals 

 is always proportionate to the resistance of the animal; in the 

 majority of cases it may serve in the course of an infection as an 

 indication of the outcome of the struggle between the bacterium 

 and the animal. So, for instance, it is more active in vaccinated 

 animals than in normal animals, whether the refractory stage be 

 obtained as a result of the injection of attenuated or sterilized 

 cultures or by means of a preventive serum. 



The existence of a peculiar reaction on the part of leucocytes to 

 chemical substances secreted by bacteria offers important evidence 

 of the part which these cells take in defense of the body.f As soon 

 as the bacteria penetrate the tissue their presence is evident from 

 the fact that their diffusible products cause a phenomenon of chemi- 

 otaxis on the part of the phagocytes. The tactile reaction of these 

 cells permits them, when chemiotaxis has been manifested and when 

 they have approached the infecting bacteria to the point of contact, 

 to send elongations about them and to engulf them. The rapidity 

 with which these various phenomena follow each other, particu- 

 larly in vaccinated animals or when dealing with slightly virulent 

 organisms, shows how active phagocytic intervention is. 



The relation between the quality, method of reaction, and number 

 of phagocytes on the one hand and the efficiency of the defense on 

 the other is shown by a series of phenomena. Leucocytes are little 

 attracted, and may even be repulsed by very virulent microbes. 



An attempt has recently been made to discredit the importance 

 of chemiotaxis in immunity. Werigo, who of course recognizes 

 the existence and the purpose of positive chemiotaxis, has certain 

 doubts as to the existence of a negative chemiotaxis. Woronin 

 goes even further. He attributes to chemiotaxis, whether positive 

 or negative, an almost negligible function in the defense of the 



* Werigo, Les globules blancs protecteurs du sang: Annales de ITnstitut 

 Pasteur, 1892. 



f J. Massart et Ch. Bordet, Journal de la Societe royale des sciences naturelles 

 et medicales de Bruxelles, 1890. 



