72 MASTITIS OF THE COW 



tions. It seldom presents chains, which are short and com- 

 posed of one or two, frequently three, individuals. The 

 bacilli often lie parallel to each other or slightly converging 

 so that gi'oups may be formed (Fig. 19) . 



It is stained with difficulty by the common anilin dyes, 

 but stains well after the method of Gram, but even here 

 one must not too strongly decolorize it with alcohol. They 

 are less Gram positive than the streptococci, but more 

 so than the malignant oedema group. 



Cultivation. — The bacillus pyogenes grows some- 

 what slowly at body temperature (38° C.) and very slowly 

 and weakly at 20° C. It does not appear to grow at room 

 temperature (15° C). It grows aerobically and anaero- 



bically, but shows more of an 

 anaerobic character. In order 

 to isolate it a pure culture 

 •^^ medium containing serum is 

 necessary, but after it has been 



Fia. 19.-Pyogenes bacilli in milk eediment. ISOlatcd it CaU bc gl'OWn OU thC 



Gram. (X 550). commou mcdla without serum. 



In serum -gelatin-agar plates at 38° C. the growth is at 

 first visible after from two to four days. The deep colonies 

 in the first plate then appear as sparse small whitish-gray 

 scarcely visible points the size of the hole made by a pin 

 prick. 



Under the microscope the colonies appear as veiy small 

 bright yellow round or rounded structureless vesicles with 

 even margins. The larger colonies appear to be produced 

 by the grouping of a greater or lesser number of these 

 vesicles into a composite mass like a raspberry and there- 

 fore present an irregular shape and a crenated margin. 

 The smaller colonies are probably produced by one bac- 

 terium, " primary or single colonies," and the larger ones 

 by coalescence of the primary colonies, " complex colonies " 

 (Fig. 20). 



