HOST SPECIFICITY 121 



Nocardia spp.), for example, are etiologically related to different 

 types of actinomycosis. The fungi which cause ringworm have cer- 

 tain peculiarities which set them apart from most of the other patho- 

 genic fungi, and because they are interrelated and the diseases they 

 cause are limited to the skin it is convenient and appropriate to refer 

 to them as the dermatophytes, and to the disease which they cause 

 as dermatophytosis. The term dermatomycosis is sometimes used 

 in the same sense, but the suffix mycosis is generally understood to 

 imply a deeper involvement than is found in dermatophytosis. An- 

 other type of mycosis which is set apart by certain characteristics 

 is the mycetoma. The various mycetomas differ in etiology, but all 

 are characterized by deep invasion of the subcutaneous tissues with 

 the formation of sinuses. In the pus which drains from these sinuses 

 the fungus is found usually in the form of rather firm, well-organized 

 granules which differ in size, shape, consistency, and color accord- 

 ing to the species of fungus involved. 



Human mycoses can be placed in two groups, those in which there 

 is only a very superficial penetration, represented by the dermato- 

 phytoses, and those involving the subcutaneous tissues and fre- 

 quently causing generalized infections, represented by a considerable 

 number of mycoses of varied types and etiologies. In any attempt 

 to generalize upon the fungus diseases this diversity must be re- 

 membered. The dermatophytoses are caused by a group of closely 

 interrelated fungi, the dermatophytes, which are physiologically 

 adapted to growth upon keratinized structures. They are able to 

 grow saprophytically upon a wide variety of animal and vegetable 

 debris, but their preference for keratinized material, their ability to 

 grow in the epidermis, frequently for long periods without actually 

 causing lesions of clinical importance, and their transmission from 

 one person to another indicate a high degree of adaptability to the 

 parasitic habit. 



Host Specificity. Some of the dermatophytes show a considerable 

 degree of host-specificity. Microsporum Audouini, for example, is 

 the species usually responsible for epidemics of ringworm of the scalp. 

 It attacks only children, causing in most cases a dry scaling lesion 

 with little host reaction. Because of its good adaptation to the host 

 it is difficult to eradicate and a single epilating dose of x-ray should 

 be given before fungicidal treatment is begun. Although the disease 

 is chronic, with little or no tendency to self-limitation in the child, 

 spontaneous cure usually occurs at puberty. It is thought that the 

 change in endocrine balance occurring at this time makes the host 



