ADDENDUM 1/3 



(b) Use of liquid blood media. A more severe test of 

 haemolysis is to test with red corpuscles in solution. The 

 method employed by Lyall and also by North, White and 

 A very was to add a definite amount (0-5 c.c.) of an 1 8 hours' 

 ascitic broth culture (ascitic fluid I part, peptone broth 5 parts) 

 to i c.c. of a 5 per cent, solution of washed sheep's red blood 

 cells and incubate in a waterbath at 37 C. for I hour (Lyall) or 

 2 hours (North, White and Avery). 



The blood-agar plate method is the simpler and the one 

 usually employed, but with its use there is some danger of 

 obtaining indefinite reactions. As Davis points out many 

 streptococci may produce a narrow, greenish, greyish or 

 brownish zone on which, especially after 2 or more days, at 

 times some clearing of the media may occur. Such strains 

 do not produce true haemolysis. 



The haemolytic test is of value since it is closely related to 

 virulence. Most of the pathogenic streptococcus strains isolated 

 from human cases of disease have been haemolytic. Apart 

 from this property it does not serve to distinguish human from 

 streptococci of animal origin. Ruediger strongly advances the 

 view that the ordinary milk streptococci can be distinguished 

 from the pathogenic types by the haemolytic tests, but the facts 

 in his 1912 paper in which he advances this view, while not 

 contradicting it do not establish any such connection. 



M'Leod in a later paper concludes that for streptococci 

 virulence and the possession of haemolytic power are closely 

 allied, if the organism is growing in the body or under 

 cultural conditions closely resembling those met with in the 

 body. 



Davis advances the view that the haemolytic test is of great 

 value in the differentiation of streptococci causing outbreaks of 

 sore throat, and points out that all the recent epidemics of sore 

 throat spread by milk in which this point has been tested have 

 been caused by streptococci of the haemolytic variety. His 

 suggestion that the types of bovine mastitis due to haemolytic 

 streptococci are those pathogenic to man, while the non- 

 haemolytic strains do not cause human disease, is very in- 

 teresting but unproved and confirmation is desirable. 



