316 BIOLOGICAL ACTIVITIES OF YEASTS 



the fruit as upon the yeasts growing there. In some insects, however, 

 the yeasts penetrate the body cavity and Uve there, probably as 

 symbionts, since they apparently do no harm to the insect, and are 

 invariably present, being transmitted in the ova. These symbiotic 

 yeasts are found particularly in the Homoptera, especially the ci- 

 cadas, and are contained in a special mass of tissue, the pseudo- 

 vitellus, so that microscopically they appear at first glance as some 

 sort of gland. The species found are for the most part members of 

 the genus Schizosaccharomyces. They have been especially studied 

 by Sulc. In another homopterous insect, the locust, there occurs a 

 pathogenic yeast which invades the blood and multiplies sufficiently 

 to make the blood a milky white color instead of its normal clear 

 straw color. It kills the insect and can be transnlitted by inoculation. 



Aside from the peculiar yeast, Nectaromyces Reukaufii, referred 

 to previously, numerous other yeasts have been found in the nectar 

 of flowers. Zinkernagel ^* has described 15 species obtained from 

 various flowers, none of which formed ascospores. Lochhead and 

 Heron,-^ studying the fermentations of stored honey, found these to 

 be due in every case to yeasts of the genus Zygosaccharomyces, which 

 could not only grow in high concentrations of honey but failed to 

 develop in media of low osmotic pressure. Thus in tubes containing 

 10, 25, 50, 65, and 75 per cent honey, fermentation occurred in only 

 the first three with "S. ellipsoideus," and it occurred only in the last 

 three with a yeast from fermented honey. An investigation of the 

 nectar of flowers showed the occurrence of similar yeasts of high 

 sugar tolerance belonging to the Zygosaccharomyces group. 



Higher animals consume yeasts with their food, and these organ- 

 isms have frequently been demonstrated in the alimentary tracts of 

 animals and man. S. guttalatus is apparently a constant normal 

 parasite of the intestines of rabbits. Most of the species found in 

 higher animals are, however, undoubtedly transitory organisms, not 

 multiplying in the body. Anderson ^ has demonstrated that most 

 species of yeasts are not injured by the digestive juices, but pass 

 through the alimentary tract, and has described a number of species 

 from human feces. Rettger, Reddish, and MacAlpine,^^ however, 

 found that baker's yeast was rapidly destroyed in the alimentary 

 tract. The occurrence of yeasts in the normal throat has been 

 studied by Tanner, Lampert, and Lampert.*® They did not, how- 

 ever, clearly distinguish the strains they isolated from Candida. 

 Yeasts were found in 10 per cent of the throats examined. Eighteen 

 of forty-seven strains were pathogenic to mice. The frequent occur- 

 rence of yeasts in or on the human body has not been sufficiently 



