THE DERMATOPHYTOSES 153 



any other tissue. These fungi for the most part produce only a 

 superficial infection, not tending to involve the deeper tissues or to 

 spread to internal organs, but they are nevertheless important because 

 of their frequent occurrence and, to a certain extent, contagiousness. 

 They are closely related species with numerous intermediary forms 

 which make up a fairly homogeneous group. They are frequently 

 referred to as the dermatophytes. 



A clear knowledge of this group of fungi can be obtained only by 

 first-hand acquaintance with them. The subject is quite complicated 

 for several reasons. Attempts have been made to classify the causa- 

 tive fungi according to the nature of the disease which they produce; 

 but the same disease may be produced by several different species 

 and, conversely, a single species is capable of producing very different 

 clinical types of disease. On the other hand, attempts at a purely 

 mycological classification based upon morphological characters has 

 been somewhat unsatisfactory because of the pronounced pleomor- 

 phism of the fungi and the incorrect interpretations and evaluation 

 of morphological features.^- ^ * The parasites exhibit a certain 

 amount of geographical specialization, some species isolated from 

 cases in one part of the world being different from those obtained in 

 other parts. Some of the parasites occur only on man, some on cer- 

 tain lower animals. The latter may be transmitted from animals to 

 man. 



A very large number of species have been described. Many of the 

 species names are synonyms and the number of true species can per- 

 haps be reduced to one tenth the reported number by a critical com- 

 parison of strains and a proper evaluation of variability. For these 

 reasons an extensive knowledge of the group can be attained only 

 after long and intensive study. The subject is one for the specialist. 

 We can do no more here than point out some of the more important 

 general characteristics of the diseases and their etiologic agents, and 

 describe a few of the more common species. 



Although a very large number of investigators have contributed a 

 voluminous literature to the subject, the work of one man, Sabou- 

 raud,^" overshadows all the rest and dominates the field. To his 

 long-continued, patient, and intensive studies we are indebted for a 

 revival of interest in the subject during the first years of this century. 

 He systematically studied different types of dermatophytosis ; cor- 

 related the clinical features, the microscopic appearance of the fungus 

 in infected hairs, and the colonial and microscopic appearances of 



* Literature citations for this section will be found on pages 177 and 178. 



