5o8 MICRO-ORGANISMS AND DISEASE [chap. 



(i) Another disease in which the presence of psoro- 

 sperms/ or at any rate of parasites morphologically related 

 to them, causes a chronic thickening and hypertrophy 

 of epithelial structures has been described by L. Pfeiffer 

 {Die jProtozoen ah Krankheitserreger, Jena, 1890) as occur- 

 ring in the fowl. This animal is occasionally found to show 

 on its skin in various parts of the body large and small 

 prominent nodules which consist of greatly hypertrophied 

 epidermis (stratum Malpighii) with corresponding infiltration 

 of leucocytes and distension of the blood-vessels of the 

 subjacent corium. The disease in question — epithelioma 

 contagiosum of the fowl — is not at all of rare occurrence, 

 and when it occurs on a farm it generally spreads to other 

 fowls. I have myself met with several such instances. 

 Sections made through the nodules show an enormous local 

 hypertrophy of the stratum Malpighii of the epidermis ; 

 and amongst the epithelial cells, in many places within these 

 cells, are found oval bodies, mostly capsulated, which are 

 distinctly of the nature of psorosperms. On staining the 

 sections in fuchsin, and then washing in alcohol or dilute 

 nitric acid, the epithelium is decolourised and leaves the 

 psorosperms stained pink ; in this manner the psorosperms, 

 with their pink protoplasm, their capsule and clear nucleus, 

 can be easily recognised. It is not a question of finding 

 such a psorospermic corpuscle here and there ; the epi- 

 thelium is pervaded by them in almost continuous masses. 

 They are found isolated within the epithelial cells, destroying 

 the substance of these latter ; or, when the epithelial cells 

 are almost destroyed over extensive areas, the psorosperms 

 are found to have entirely replaced them. There is not the 



' The following account is an abstract of my Report on " Psorosperms 

 in their Relation to the Etiology of Cancer " in the Reports of the Medical 

 Officer of the Local Government Board for 1893-1894, pp. 479, &c. 



