140 



In order to give an impression of the different appearances 

 colonies of various strains of Pfeiffer's bacillus may present, photo- 

 graphs are reproduced in plate 2, of colonies of 15 strains of 

 Pfeiffer's bacillus (as well as a colony of Bacillus haemoglobinophilus 

 canis). In each case the inoculation was made (Nov. 1921) on 

 FiLDEs-agar, and the plates were then kept in the incubator for 

 about 2 days. There were colonies on all the plates which were 

 so isolated from the rest that they could not have been inhibited 

 by their neighbours to any appreciable extent as regards the full 

 development of their size and morphological characters. Square 

 pieces of the agar with such colonies were cut out, placed together 

 on a slide, and photographed by transmitted light and with a mag- 

 nification, x 10.* The first thing that will be noticed is the very 

 unequal size of the colonies. The thickness of the medium was 

 certainly not uniform, varying from 2—3 mm. This is however 

 far from sufficient to explain the difference in the size of the 

 colonies. In 4 cases the layer of agar was 2 mm. in thickness 

 and the colonies represented from these plates were 1.7, 1.8, 1.8, 

 and 3.3 mm. in diameter. In 6 cases the layer of agar was 2V2 nun. 

 thick and the colonies were. 1.2, 1.3, 1.7, 2.3, 2.4, and 3.2 mm. in 

 diameter. In 5 cases the figures were 3 mm. ond 2, 2.1, 3.0, 3.3, 

 and 5.5 mm. respectively. 



Marked differences will also be observed in the degree of 

 translucency and internal structure. 



It is not a question of fortuitous characters of the indi- 

 vidual colony, as each of the plates displayed a homogeneous 

 and characteristic appearance both on macroscopic inspection 

 and on examination of the different colonies with a weak mag- 

 nification. 



Most of the strains had been examined twice before in 

 the same way. 



(For the first of these two examinations („I") which took place 

 in Jan. 1920, agar containing haemolysed blood was used, and for 

 the second („II"), in Sept. 1920, FiLDES-agar). 



The appearance of the individual colonies depicted will now 

 be described and also compared with the records of the ap- 

 pearance of the colonies of the same strains in the earlier 

 investigation. Included in the description is a phenomenon 

 which in consequence of the weak magnification is not so 



* In the reproduction, the medium around the colonies is replaced 

 by a uniform back-ground. 



