32 



QUATERCENTENARY STUDIES IN PATHOLOGY 



then introduced into each tube. The tubes are placed in the incubator 

 at 37° C, and are examined at stated intervals, say in 3, 16, 24-48 hours, 

 the same volume from each tube being pipetted on to an agar tube or 

 Petri dish. The absence or diminution in the number of colonies on 

 these tubes or plates after their incubation is, with certain reservations, 

 regarded as the indication of bacteriolysis having taken place. The 

 condition of the small test tubes, after their incubation for 24-48 hours, 

 affords valuable information, as will be exemplified in the following test : 

 Test of the Serum of Horse " RD." — The arrangement in thia experi- 

 ment was as above. The bacterial dilution was prepared by emulsifying 

 a 2 mgm. ose from a 24 hours culture on agar of a highly virulent plague 

 bacillus in 10 c.c. of normal salt solution ('85%). The bacilli were well 

 distributed by shaking, and a 2 mgm. loopful of this dilution was introduced 

 into each of the tubes containing the immune serum, fresh horse serum 

 and broth. The agar tube planted at once from the control tube, which 

 contained salt solution and bouillon but no serum, gave a fair number of 

 colonies, which became confluent over the water of condensation. A 

 measured quantity from each tube was planted on agar, after 3 and after 

 16 hours. The details and result of the experiment are shown in the 

 Table XX. 



TABLE XX. 



(142) 



