PLANT PARASITES. 161 



mouth and fauces and oesophagus of children, in the form, of a whitish 

 pellicle aphthre is the so-called Oidium albicans, which consists of 

 branching, jointed threads and spores which penetrate between the epi- 

 thelial cells. This fungus may assume considerable importance, when 

 in very feeble children it blocks the oesophagus, or when, as is rarely the 

 case, from the surface of ulcers it penetrates the blood-vessels and gives 

 rise to visceral metastasis. The exact relationship of this fungus to the 

 moulds is not yet very clear. It is often grouped with the yeasts. ' 



Methods of Studying Yeasts and Moulds. 



The yeast organisms are in general stained and cultivated by the same methods as 

 those used in studying the bacteria. By treating unstained sections of tissue contain- 

 ing them with solution of caustic potash the organisms may often be readily demon- 

 strated. 



The moulds may be simply teased and studied in glycerin or in glycerin and water. 

 They may be stained with alkaline-methylene blue solution (Loffler's solution, see page 

 154). When spores have formed in considerable numbers on the more complex forms 

 of moulds these are not easily wetted by the usual staining fluids, because the air clings 

 so closely among the spore masses. In a mixture of four parts of alcohol and one of 

 aqueous solution of ammonia they are instantly wetted, and may then, with or without 

 staining, be teased and mounted in glycerin. In studying the fungus masses in the 

 above -described skin diseases it is well, when crust-like masses are to be teased apart, 

 to allow them first to soak for a few moments in a five-per-cent solution of caustic 

 potash. In this solution they may be studied, or they may be teased and mounted in 

 glycerin for preservation. Most of the more common moulds are readily grown on the 

 ordinary culture media. 



1 For resume and bibliography of relationship of yeasts and moulds to human dis- 

 eases consult Kicker, Lubarsch, and Ostertag's " Ergebnisse der allg. Aetiologie der 

 Menschen u. Thierkrankheiteh," Abth. i., 1896, p. 892. See also Hektoen, Journal of 

 Experimental Medicine, vol. v., p. 77, 1900. 



11 



