PARASITES OF ACTINOMYCOSIS 659 



2. In cultures. The appearance of the parasite in cultures is quite different 

 from its appearance in the tissues. Branched filaments, coccal forms and 

 short rods are found, but no clubs are seen. In young cultures the mycelium 



FIG. 310. Discomyces bovis. Section through an human lesion. Gram's 

 stain and eosin. (Oc. 2, obj. J*th, Zeiss.) 



consists of delicate, branched, non-septate filaments which are sometimes 

 very long. In older cultures these filaments divide into short stout rods 

 (bacillary and coccal forms) ; the aerial hyphse are thick and carry chains of 

 conidia. In very old cultures, swollen and irregular-shaped involution forms 

 are found. 



B. Cultural characteristics. 



Conditions of growth. Discomyces bcvis grows equally well under aerobic 

 or anaerobic conditions. Growth commences at 20 C. is most luxuriant 

 at 37 C., less abundant at 40 C., but still continues up to about 50 C. 

 Most of the ordinary media are suitable for the cultivation of the parasite, 

 the best growths however are obtained on serum and on media containing 

 glycerin. 



Some difficulty is often experienced in isolating the parasite from pus 

 because in most cases it is associated with the ordinary organisms of suppura- 

 tion, and these grow over the culture medium before the discomyces has had 

 time to start. There are several methods of isolation, the most satisfactory 

 being that described by Bostrom. 



Spread the pus containing the yellow grains on plates of gelatin and incubate 

 for a couple of days. On then examining the plates most of the grains will be sur- 

 rounded by colonies of contaminating organisms but a few will be seen here and 

 there which are more or less discrete and isolated. Pick these off with a stout 

 platinum wire and transfer them to tubes of coagulated serum and incubate the 

 cultures at 37 C. After 5-6 days the colonies of discomyces begin to grow. If 

 this method be adopted it is advisable to sow a good number of tubes of serum 

 because many of them will ultimately prove to be contaminated. 



Culture media. Glycerin-broth. When sown and incubated at 37 C. 

 white, granular, hemispherical colonies appear in about 5 or 6 days and may 

 grow as large as a pea. The colonies fall to the bottom of the tube leaving 

 the medium quite clear. 



Coagulated serum. After being incubated for about 5 days, small whitish 

 or yellowish colonies appear, dry, firm, and often confluent. 



