328 ACTINOMYCOSIS AND ALLIED DISEASES 



growth occurs or it is of a very slight character. On the surface 

 of agar under anaerobic conditions the organism produces dense 

 rounded colonies of greyish-white colour, which sometimes 

 assume a rosette form. A, somewhat curious feature of growth 

 is described by Wright, namely, that in a shake culture in 

 glucose agar the colonies are most numerous and form a dense 

 zone about half an inch from the surface of the medium, that 



is, at a level where there 

 is presumably a mere 

 trace of oxygen obtain- 

 able (Fig. 95). In 

 bouillon, growth takes 

 place at the bottom of 

 the medium in rounded 

 masses which afterwards 

 undergo disintegration. 

 Wright found that, when 

 the organism was grown 

 in the presence of serum 

 or other animal fluids, 

 the formation of true 

 clubs occurred at the 

 extremity of some of 

 the filaments (Fig. 96). 

 From the conditions 

 under which growth 

 occurs, he is inclined to 

 regard it as a true para- 

 site, and doubts whether 

 it can have a sapro- 

 phytic existence outside 

 the body, e.g., on grain. 

 He is also of opinion 

 that all cases of true 

 actinomycosis, i.e., cases 

 where colonies visible to the naked eye are present, are prob- 

 ably produced by one species, and that the aerobic organisms 

 obtained by Bostrom and others are probably accidental 

 contaminations. 



The views' of Wright are supported by the recent observations 

 of Harbitz and Grdndahl on actinomycosis in Norway. They 

 obtained pure cultures from ten different cases, and in each 



1 For Figs. 95 and 96 we are indebted to Dr. J. Homer Wright of 

 Boston, U.S.A. 



w 



Fig. 95. 1 — Shake cultures of actinomyces in 

 glucose agar, showing the maximum growth 

 at some distance from the surface of the 

 medium. 



