180 G. G. Heslop: 



Microscopic Method. 



In order to test whether the usual microscopic method of ob- 

 serving the agglutination reaction could furnish any additional 

 evidence over the macroscopic method, two hanging-drop pre- 

 parations were made under cover slips on hollow glass slides,, 

 the cover slips being ringed round with vaseline in order to pre- 

 vent evaporation of the hanging drops. One hanging drop con- 

 sisted only of pure culture of the organism in Martin's broth, 

 plus ox serum, and on microscopic examination showed no trace 

 of any recognisable micro-organisms when using the highest mag- 

 nification available (1000 diameters). The other hanging drop- 

 consisted of a mixture of the same culture, and a positive serum 

 in the proportion of 2 parts of culture to 1 part of serum dilu- 

 tion, serum No. 12 being used. " This preparation was examined 

 microscopically at various intervals extending over 4 hours, but 

 at no time could any alteration in the appearance of the hang- 

 ing drop be observed. No difference in appearance under the 

 microscope could be noted when the hanging drop containing 

 culture and serum was compared with that containing culture 

 only. 



In order to have a further means of comparison it was de- 

 cided to repeat this hanging drop test, and to control it more effi- 

 ciently, two additional hanging drop preparations were put up. 

 Thus we had for examination four hanging drop preparations, 

 containing the following ingredients respectively: — 



Hanging-Drop Preparation No. 1, containing culture only. 

 Hanging-Drop Preparation No. 2, containing culture (2 



parts), and serum dilution (1 part) ; the serum being 



Serum No. 12 (positive serum). 

 Hanging-Drop Preparation No. 3, containing culture (2 



parts), and serum dilution (1 part); the serum being 



Serum No. 30. 

 Hanging-Drop Preparation No. 4, containing culture (2 



parts), and serum dilution (1 part); the serum being 



No. 17 (negative serum). 

 Serum No. 30 was the serum from Experimental Calf 1, which 

 had previously given a positive agglutination reaction when tested 

 by the macroscopic method. 



Serum No. 17 was a negative serum, and had previously given 

 a negative agglutination reaction when tested by the macroscopic 

 method. The preparations were examined microscopically at 



