704 THE PARASITIC YEASTS 



pearly colonies appear which however never attain any large size. The 

 medium is not liquefied. 



Agar. At 37 C. on agar there is a rapid growth of white smooth spreading 

 colonies. 



Potato. Small raised colonies, dirty white in colour and occasionally 

 spotted with black. 



Carrot. On slices of carrot, the fungus forms an abundant shiny white 

 growth in 48 hours. 



Broth, sterile wine, and Nsegeli's medium. Small white masses, the liquid 

 itself remaining clear. 



3. Biological .proper ties. The virulence of the organism in cultures is very 

 variable : it is attenuated by growth on artificial media and is increased by 

 passage through animals (Roger and Grasset). 



Cultures contain toxins (Charrin and Ostrowsky) but no immunizing sub- 

 stances. Rabbits can be immunized by inoculating them sub-cutaneously 

 with increasing doses of attenuated living cultures or by intra-venous inocula- 

 tion of increasing doses of such cultures. The serum of immunized animals 

 exhibits agglutinating properties (Roger). 



SECTION II. THE GENUS SACCHAROMYCES. 



1. Saccharomyces tumefaciens (Curtis). 



Curtis isolated a parasite, to which he gave this name, from a case of myxo- 

 matous tumour of the thigh in a man. 



1. Experimental inoculation. Mice, rats and dogs are all susceptible to 

 infection. 



Following the sub-cutaneous inoculation of a small number of the parasites 

 into rats or mice a tumour similar to that occurring in man is formed. The 

 tumour attains enormous dimensions and the animal may die after a con- 

 siderable time, but the fungus never passes into the blood-stream. Occa- 

 sionally, neoplasms form in all the internal organs which appear as though 

 sprinkled with small white dots. In the tumours the parasite is always found 

 in pure culture. 



In rabbits, intra-venous inoculation has negative results, while sub-cutaneous 

 inoculation produces a small abscess which undergoes spontaneous resolution. 



Guinea-pigs are practically immune. It is, 

 however, possible to infect them by using a 

 strain the virulence of which has been raised by 

 growing it in collodion sacs in the peritoneal 

 cavities of guinea-pigs (Wlaef). The inoculation 

 of such cultures beneath the skin produces 

 lesions in the skin, and occasionally a generalized 

 infection. 



2. Microscopical appearance. In the tissues 

 S. tumefaciens is encapsulated, but in cultures 

 the capsule is generally absent. 



(a) On agar at 37 C. after incubating for 



. Saccharomyces tume- 48 hours growth consists of round or ovoid 

 Culture n agar> (After cells from 3-6/x in diameter, surrounded by a 

 double -walled membrane and containing one or 

 two refractile granules : in young cultures the ovoid cells are more numerous 

 than the spherical cells and nearly all of them have a small bud at one end. 

 Methyl violet 6B stains the centres of these cells deep violet and the wall 



