196 



INFECTIONS CAUSED BY MOLDS 



smooth, moist and shiny without developing the cottony masses of 

 aerial mycelimn seen in most molds. Other strains develop a short 

 black aerial mycelium which may be more abundant on some media 

 such as prune agar, and which may be aggregated into coremia-like 

 structures which give the surface of the colony a spiny appearance. 

 If some of this growth is examined under a microscope there are 

 found a tangled mass of branched mycelium and a large number of 

 pear-shaped conidja which are almost all freed from the hyphae 

 when material is mounted for examination in the usual manner. To 



see their normal relationship it is 

 necessary to prepare slide cul- 

 tures. This was done by de 

 Beurmann and Gougerot ^ by 

 placing sterile slides in wide test 

 tubes with a small amount of 

 dextrose broth into which the 

 organism was inoculated. As it 

 grew, the mold would climb the 

 slide for a short distance, and 

 the slide was then removed and 

 the growth fixed and stained. 

 The methods of slide culture 

 preparation described in Chap- 

 ter I are preferable. In such a 

 preparation some of the conidia 

 will remain in place at the tips and along the sides of simple conidio- 

 phores and on the undifferentiated hyphae. Each conidium is at- 

 tached by a very narrow stalk which, when it breaks, remains in part 

 on the pointed end of the conidium and in part as an apiculate scar 

 on the hypha from which the conidium fell. This stalk may appear 

 almost thread-like in specimens which have been dehydrated and 

 stained. Conidia which have fallen to the surface of the culture fre- 

 quently bud to produce secondary conidia which are borne on narrow 

 sterigmata. Chlamydospores are also produced on the mycelium. 



Both cultural and morphological characters are subject to consider- 

 able variation. Of the former, the degree of pigmentation is most 

 variable. Some strains may never develop more than a light tan 

 color, others may darken very rapidly. The same strain may form 

 more pigment' on some media than on others, or on the same medium 

 may remain colorless at one time and become pigmented in a later 

 transfer. An inoculation of a pure culture on agar may show pig- 

 mentation in one portion of the colony and none in another. 



Fig. 100. Sporotrichum Schenckii. 

 Conidia in culture. 



