14 An Introduction to Medical Mycology 



obtained from patients who were suffering from a variety of superficial 

 ringworm infections. The negative results showed the test to be valueless 

 here and indicated that few or no antibodies develop in the course of super- 

 ficial ringworm. 



9. FUSION OF MYCELIUM 



This method was devised by Davidson and his co-workers to establish 

 the identity of an unknown species. Only strains of the same species will 

 fuse with each other when myceliums of two or more species are allowed 

 to mingle. The myceliums of two strains of M. lanosum fuse, but no fusion 

 takes place between M. lanosum and Microsporum audouini. 



10. HISTOLOGIC EXAMINATION 



This reveals the nature of the reaction of the host to the invasion of the 

 pathogenic micro-organisms. The fungi themselves are rarely seen. In the 

 superficial chronic infections the lack of pathologic changes may be help- 

 ful in the differential diagnosis from other dermatoses. In the deep forms 

 of infection, there is no specific picture and granulomatous changes are 

 the rule. Moore showed the close similarity between tuberculosis and many 

 of the deep invasive fungous infections. In the acute form of each, a highly 

 inflammatory reaction occurs, often leading to abscess formation. In the 

 chronic forms, there are granulomas containing giant cells arranged in 

 tubercle-like formation and plasma, epithelioid, lymphoid and polymor- 

 phonuclear cells. In fungous disease there are usually fewer epithe- 

 lioid cells and more plasma and polymorphonuclear cells than in tuber- 

 culosis. 



In some cases, histoplasmosis may only be established by postmortem 

 examination of internal organs or tissues. 



11. THE THERAPEUTIC TEST 



When the diagnosis cannot be definitely established but the clinical 

 features point to a fungous disease, it may be considered expedient to 

 institute therapy. Improvement of the disorder following fungicidal ther- 

 apy is evidence that the disease is mycotic. We advise against beginning 

 therapy before the diagnosis is established by recognized laboratory meth- 

 ods. It is thus frequently advisable to delay treatment for several days or 

 even weeks. 



