126 FUNGUS DISEASES OF MAN AND ANIMALS 



sis. Other fungi appear to require introduction to the subcutaneous 

 tissues through wounds. 



Some species of pathogenic fungi have a very low invasive power. 

 In fact, in some of the so-called fungus infections there is no infec- 

 tion in the strict sense, for the parasites do not invade the tissues 

 except to grow in the most superficial epidermal layers. This is true 

 of tinea versicolor; and in many cases of otomycosis the fungus 

 hardly invades the epithelium of the ear but grows as a saprophyte 

 upon the ear wax. In dermatophytosis and in most cases of thrush 

 the fungi invade principally the epithelium and rarely penetrate 

 beyond it. 



Pathological Anatomy of Mycoses. In the generalized mycoses 

 already mentioned extensive and deep-seated lesions may occur and 

 the disease may spread to other parts of the body either by way of 

 the lymph vessels or the blood stream. The tissue changes brought 

 about in these cases are in part of the nature of abscesses, and in 

 part of the nature of granulomata. Immediately surrounding the 

 parasite there is usually death of the tissues, with softening and the 

 accumulation of leucocytes and the formation of pus. ]\Iany of these 

 abscesses become surrounded by granulation tissue consisting of a 

 dense layer of new fibrous tissue infiltrated with, mononuclear leuco- 

 cytes and sometimes containing giant cells. The degree to which 

 one or the other of these processes predominates varies with the 

 virulence of the strain and the mode of infection. Thus the primary 

 lesions of blastomycosis in the skin are mainly granulomatous, the 

 secondary lesions following a blood-stream distribution are usually 

 pure abscesses. In animals experimentally inoculated with rather 

 large doses, pure abscesses similar to those produced by the pyogenic 

 cocci usually develop. However, in some human infections the lesions 

 may so closely resemble various granulomatous processes, such as 

 those of tuberculosis and syphilis or even cancer, as to make the 

 diagnosis difficult. In experimental infections in laboratory ani- 

 mals the type of lesion may vary widely with the dosage and mode 

 of inoculation. Thus if large doses of Aspergillus fumigatus spores 

 are injected intravenously into pigeons, areas of necrosis with hemor- 

 rhage and very little cellular infiltration will develop about the 

 germinating spores. With very small doses one gets typical tubercles 

 in internal viscera after a much longer time (see Fig. 110). If one 

 blows a mass of spores into the trachea, there develops an acute 

 pneumonia fatal within 24 hours, whereas, if the pigeons are fed on 

 infected grain so that only an occasional spore is inhaled from time 



