492 PATHOGENIC BACTERIA. 



leukocytes is a matter of interest. Achard and Bensaud ' 

 have decided that there is no relation between the two. 

 They experimentally secured plasma devoid of leuko- 

 cytes by using leeches and centrifugation, and found it 

 active, and also secured leukocytes by filtering the fluid 

 through cotton. The living active leukocytes did not 

 cause any phenomenon on the part of the bacilli when 

 brought into contact with them. 



VIII. The Relation of Agglutinating Power to Im- 

 munity. There are numerous reasons for regarding the 

 reaction as one of immunity, and many able men, among 

 whom are Maragliano and Pfeiffer, adhere to this view. 

 It is well known that the reaction usually develops some 

 days after the inception of the disease, is most marked 

 during the third week, and remains as a post-typhoid con- 

 dition for about the length of time that immunity to the 

 disease is supposed to exist. This looks significant, and 

 is at least interesting, if of no especial importance. 



The reaction is also observed to be less intense in mild 

 than in severe cases, though there are numerous excep- 

 tions to this. Achard 2 noticed that after relapses the 

 agglutinative power of the serum was increased. In 

 some of their writings, Widal and Sicard look upon the 

 reaction as one of defence on the part of the organism, 

 especially during the period of infection. Charrin also 

 shares this opinion. 



In the so-called vaccination against typhoid fever prac- 

 tised by Wright and Semple, the prophylactic injections 

 of sterilized cultures of virulent typhoid bacilli beneath 

 the skin impart to the blood of the individual a more or 

 less marked immunity, the occurrence of which it is sup- 

 posed can be gauged by observing when the agglutinative 

 power of the blood occurs. 



Welch points out that in experimental immunity to 

 typhoid, in which there is an increase of immunity to 

 great heights, there may be a corresponding rise of the 



1 Semaine med., 1896, p. 393. 



1 Bull, de la Soc. mid. des Hop., Oct. 16, 1896. 



