500 PATHOGENIC BACTERIA. 



The more actively motile the bacilli, the greater the con- 

 trast when this motility ceases ; the longer the bacilli, 

 the more typical are the agglutinations. Cultures less 

 than twenty-four hours old are best. At a pinch, how- 

 ever, they can be employed so long as they remain motile 

 (forty-eight hours). 



2. Activity. — Johnston first pointed out that virulent 

 bacilli frequently transplanted from culture-medium event- 

 ually developed an abnormal condition in which reactions 

 were apt to occur with normal blood. The best method of 

 avoiding this error seems to be to keep a stock culture in 

 the laboratory, and transplant it from agar to agar only 

 as often as is necessary to keep it in good condition — say, 

 once in three or four weeks. A transplantation from this 

 to whatever culture-medium is preferred is made about 

 twenty-four hours before testing. 



3. Virulence. — Johnston is emphatic upon the use of 

 attenuated rather than virulent, freshly-isolated cultures, 

 stating 1 that "with virulent cultures the presence of 

 agglutinative substances in non-typhoid bloods may lead 

 to pseudo-reactions. " These reactions are characterized 

 by a rapid clumping without the characteristic loss of 

 motion. Kuhnan 2 seems to differ with Johnston, how- 

 ever, and finds that the reaction with non-virulent cult- 

 ures is nearly double that obtained with virulent ones. 

 Foerster 3 did not observe that the difference between the 

 reaction obtained with virulent and attenuated bacilli 

 was great. He experimented with nine different bacilli, 

 and expresses the difference observed as 5 : 8. 



4. Reaction of the Culttire-medinm. — Johnston also in- 

 vestigated this subject, and found that when the bacilli 

 are cultivated upon acid media they may entirely lose 

 their ability to agglutinate. Care should be taken to 

 insure that the culture-medium employed always has the 

 same degree of alkalinity. On the other hand, the media 



1 Montreal Med. Jour., Mar., 1897. 



1 Berliner klinische Wochenschrift, May 10, 1897, No. 19. 



3 Zeitschrift f. Hygiene, 1897, vol. 24, p. 500. 



