KEY TO THE DERMATOPHYTES 



161 



if one has also seen the patient, but the final identification of species 

 rests upon an examination of a pure culture. In using Sabouraud's 

 system of differentiation, it is obvious that the inspection of hairs is 

 necessary. For this purpose it is of course necessary to select dis- 

 eased hairs. Selection may be facilitated by search under Woods 

 light.^ Too frequently a bunch of 

 perfectly normal hairs is sent to 

 the laboratory for diagnosis ! The 

 fungus is found in the lower part 

 of the hair, that which is within 

 the follicle and extends for a rela- 

 tively short distance above the skin 

 level. Hairs which have broken 

 are of course more likely to show 

 an extensive development of the 

 organism than those which are not. 

 Infections with Trichophyton 

 tonsurans cause the hairs to break 

 off flush with the skin, the stumps 

 appearing as black dots in the fol- 

 licles. These should be extracted 

 with forceps for examination. In 

 all cases the fungi first invade the 

 hairs in the sheath. Whether even- 

 tually it will be found within the 

 shaft or without would appear to 

 depend largely upon the duration 

 of the infection, which in turn is 

 correlated with the degree of in- 

 flammatory reaction. In any case, it is well to remember that the 

 differentiation according to position of the fungus in or on the hair 

 is not an absolute one. In endothrix forms there will be some spores 

 outside the hair, in ectothrix types some within. 



Fig. 80. Diagram showing the rela- 

 tions of ringworm fungi to the hairs: 

 a, Microsporum; b, Endothrix Tri- 

 chophyton; c, Ectothrix Trichoph- 

 yton. 



KEY TO THE DERMATOPHYTES 



Lesions of the Scalp 



Yellow crusts or scutula present. Clinical favus. 



1. Hairs tend to split longitudinally. Colonies waxy, wrinkled, little or no 

 aerial mycelium. Hyphae coarse, distorted, tips swollen and branched. 

 Few conidia, no macroconidia. Trichophyton Schoenleini 



2, Colonies white, downy. Conidia and macroconidia formed. 



Trichophyton quinckearium 



