436 BACTERIA PATHOGENIC TO MAN 



by Unna to'growtr/ atjlie sides proceeding more vigorously than at the 



centre. 

 There is some difference of opinion as to whether there is only one 



or several varieties of favus fungus. It was suggested by Quincke that 



there are three different species of favus 

 fungus. Later investigations have appa- 

 rently shown, however, that the achorion 

 Schoenleinii is the only fungus of favus. 



The favus fungus is readily cultivated at 

 the body temperature, and also at room 

 temperature, in the ordinary culture media, 

 as agar, blood serum, gelatin, bouillon, 

 milk, infusion of malt, eggs, potato, etc. 

 (Fig. 138). The growth develops slowly 

 and shows a preference to grow beneath 

 the surface of the medium except on 

 potato, upon which it develops on the sur- 



Five-months-old colony of favus on ^ -, L rp,, , . ,. 



peptone-maltose agar; actual size. face m layers. Ihe characteristic torm ot 



growth is that of moss-like projections 



from a central body. The color is at first grayish- white, then yellowish. 

 As seen under the microscope, ray-like mycelium filaments are devel- 

 oped, which divide into branches. The ends are often swollen or 

 club-shaped, and there are various enlargements along the body of 

 the filament. 



Pityriasis Versicolor. 



This organism belongs to a group of fungi which, in contrast to the 

 more parasitic fungi, favus and trichophyton, invades only the most 

 superficial layers of the skin. It does not penetrate the deeper layers 

 nor does it give rise to any considerable pathological changes in the 

 skin or hair. Although the vegetative elements of these fungi are much 

 more numerous in the affected portions of skin than is the case with 

 the more parasitic species, they are not nearly as contagious as the 

 latter. 



By preference pityriasis versicolor attacks the chest, abdomen, back, 

 and axillse; less frequently neck and arms, while exceptionally it attacks 

 also the face. The growth shows itself as scattered spots varying in 

 color from that of cream-coffee to reddish-brown. The spots are 

 readily scraped off and show fine lamellation or scaling. Occasionally 

 the spots are confluent, and sometimes arranged in ring form like herpes 

 tonsurans. 



In spite of their slight contagiousness this is one of the most frequent 

 dermatomycoses. Although it is distributed widely over the earth, it 

 is more frequently observed in southern than in northern countries. 



Persons with a tender skin and a disposition to perspire freely are 

 particularly affected by pityriasis versicolor, and this is undoubtedly the 

 only reason why the affection is so frequently observed in consumptives. 



