642 PATHOGENIC MICROORGANISMS 



another, owing to the fact that selective cultivation has succeeded in 

 altering many of the characteristics displayed by many of the strains. 

 The same observer recommends the following method for obtaining pure 

 cultures of this microorganism. As much of the material as can be 

 conveniently obtained is gently rubbed up in a sterile mortar with fine 

 sand or infusorial earth. The triturated material is then inoculated into 

 fluid agar and plates are poured. 



Ordinary streaked plates upon agar may also be used with success 

 with material directly from the centers of scutula. 



The achorion grows best upon acid agar at a temperature of 37.5° G. 



Fig. 161. — Thrush. Oidium albicans, unstained. (After Zettnow.) 



Growth appears within from forty-eight hours to three days as yellowish 

 disks, which occasionally may be sUghtly furred with aerial hypha. 



Ringworm (Trichophyton tonsurans). — Ringworm, Tinea circinata, 

 or Herpes tonsurans, is a contagious disease of the skin and hair, occur- 

 ring most often in children and appearing upon both the haired portions 

 of the body, as well as upon free skin. It is characterized by the forma- 

 tion of circular scaly patches, within which the hairs fall out. 



The disease is caused by several species of the trichophyton, a genus 

 of hyphomycetes. These microorganisms were first recognized as inci- 

 tants of the disease by Gruby^ in 1841, and were most thoroughly 



• Grvby, Comptes rend, de I'acad. des soi., 13, 1841. 



