CHAPTER XXV 



Microscopic Characteristics of the 

 Dermatophytes 



WHEN specimens of a fungus colony are examined, various vegeta- 

 tive and reproductive forms may be distinguished. Only vegetative 

 forms are seen at the periphery of the colony; the spores (reproductive) are 

 to be found toward the center or at the base. These microscopic features are 

 dissimilar in different genera, and frequently there are minor variations in 

 species. The variations, however, may result from conditions of growth 

 rather than arise as specific characteristics. In most instances the gross 

 appearance of a colony is sufficient to identify the micro-organism provided 

 the observer is familiar with the medium on which the fungus is growing. 

 Confirmation of the cultural diagnosis is the chief purpose of the culture 

 mount in routine practice. 



1. VEGETATIVE FORMS 



(a) Mycelium, hyphae and thallus.— These terms indicate threadlike 

 sterile organic material, which may be septate or nonseptate and may be 

 present in large or small masses. 



(b) Pectinate bodies.— These are seen as "broken comb'' unilateral pro- 

 jections. This form is characteristic of M. audouini, A. schoenleini and T. 

 gypseum. 



(c) Racquet mycelium (mycelium en raquette).— The hyphae show 

 regular enlargement of one end of each segment. They are usually larger 

 than other hyphae. They can usually be seen in any species of Microsporum, 

 in E. inguinale and in T. gypseum. 



(d) Resorption of protoplasm.— The protoplasm constituting the con- 

 tents of the mycelium may be irregularly distributed. This characteristic is 

 emphasized by staining the preparation. 



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