170 BACTERIOLOGICAL EXAMINATION OF WATER. 



the identification of Eberth's bacilli are often quoted. The 

 agglutination tests were made in a series of tubes of small 

 calibre, so that each tube held a column of fluid from J to 1 c.m. 

 in height. The serum was added to the culture contained in 

 the tubes, which were then incubated at 37 to 40 C. After 

 thirty to forty minutes the tubes were examined with the naked 

 eye. The anti-typhoid serum employed was extremely powerful, 

 having been obtained by injecting a horse for two years with 

 cultures obtained from the same specimen of B. typhosus. The 

 results obtained are shown in the table on page 169. 



The cultural characteristics of these various bacilli were care- 

 fully studied, and Van de Velde found that the bacilli which 

 corresponded in their cultures to the B. typhosus were those 

 which were agglutinated by very small doses of the anti-typhoid 

 serum. The culture " Berlin " was the only exception, and this on 

 further study was found to give an indol reaction in Witte's pep- 

 tone solution, so it was excluded from the list of true typhoid 

 organisms. On the other hand, all the bacilli which corresponded 

 to the cultures of B. coli were not agglutinated by the anti- 

 typhoid serum. 



Beco"s researches on the value of agglutination by anti-typhoid 

 serum as a means of diagnosis between the B. typhosus and coli- 

 form races form a strong contrast to Van de Velde's experiments. 

 Beco employed young broth cultures of B. typhosus and diluted 

 the anti-typhoid serum with distilled water or physiological 

 fluid. A known quantity of the culture was distributed amongst 

 a series of glasses, and the serum was added with a sterilised 

 pipette so as to give the dilutions mentioned in the table. The 

 glasses were examined by the naked eye, and from time to time 

 a loopful was taken and examined in a hanging drop ; at the 

 end of two hours the test was considered finished. When 

 agglutination occurred the homogeneous aspect of the culture 

 disappeared and small granular masses were seen in the fluid ; 

 the appearances in the hanging-drop agreed with the changes 

 observed by the naked eye. The specimens were also submitted 

 to the action of formalin according to Malvoz\s technique. Beco's 

 results are shown in the following table : 



