120 PHYSIOLOGY OF YEASTS (Continued) 



are unfavorable to the formation of ascospores, while the rays with 

 longer wave lengths, having a lower chemical energy, have little in- 

 fluence and permit the formation of ascospores. 



Acid or Alkaline Media: The investigations of Saito have shown 

 that the degree of acidity or alkalinity determines sporulation and an 

 increase in acidity or alkalinity is accompanied by a retardation in 

 the formation of ascospores. The higher limits of acidity for Zygosac- 

 charomyces Mandshuricus on plaster blocks are 0.5-1.0 per cent of sul- 

 furic acid, malic acid, tartaric or citric acid. The higher limits of 

 alkalinity are 0.2 to 0.4 per cent of sodium hydroxide. Certain toxic 

 substances also affect the sporulation. 



Osmotic Action: This also exerts an effect on sporulation. The 

 maximum concentration for spore formation in a yeast depends upon 

 the species. For an osmophilic species like Zygosaccharomyces Mand- 

 shuricus the concentration is high. In a substrate with 25 per cent of 

 salt this yeast still sporulates. The investigations of the action of other 

 salts towards this yeast give data which depend upon the nature of 

 the salt. Thus, a very concentrated solution of potassium nitrate 

 has much less effect than isotonic solutions of NaCl. On the other 

 hand, the method of using the substance also determines the results. 



Parasitism of the Yeasts. Pathogenic Properties. Symbiosis 



Quite a number of the yeasts are parasites. They seem to have 

 received less attention than the other vegetable parasites. It is only 

 with animals and man that the parasitism in the yeasts is of any im- 

 portance. Endomyces albicans, a fungus related to the yeasts, has 

 been known for a long time to cause lesions in man. Remack has found 

 in the intestines of mammals a true yeast capable of sporulation which 

 received the name of Saccharomycopsis guttulatus. Metschnikoff in 

 1884 discovered in the general cavity of a crustacean (Daphnia) a yeast 

 which caused a special infection. It was by means of this yeast, on 

 account of the thin wall of the daphnia, that Metschnikoff discovered 

 phagocytosis. The yeast was called Monospora cuspidata. 



Other pathogenic yeasts have been observed in other animals. 

 Biitschli and Dangeard have found them in the Anguillula, Schaudin 

 in the intestines of Culex and Lindner in the larvae of the fly Core- 

 thra plumicorum. 



For a dozen years the number of pathogenic yeasts has been 

 notably increased by the discovery of different ones which cause 

 various troubles in man and animals under the name of blastomyco- 

 sis. Rivolts and Micellone have described the Cryptococcus farcimi- 

 nosus which causes farcy in the horse. Raynaurd, Lucet and Guegen 



