36 University of California Publications in Zoology ["Vol. 11 



inclined to believe the infection spreads largely by the ingestion 

 of virulent material, as we have seen fowls eat the scabs which 

 fall to the ground and also pick them from the heads of their 

 infected neighbors. 



PATHOLOGY 



Introduction. — The etiological agent of epithelioma eon- 

 tagiosum has long been thought to be contained in the cell 

 inclusions mentioned by every one who has studied the disease. 

 There is no question but that the causative agent is contained 

 in the epithelial growths since the disease is so readily trans- 

 mitted by the introduction of even a very minute quantity of 

 the growth into a healthy fowl. Since, from the standpoint of 

 its transmissibility, the disease is so evidently infectious, one 

 would naturally expect to find a specific organism in the lesions 

 produced. 



With the above idea in mind, one is naturally struck by the 

 constantly appearing cell inclusions in the epithelial overgrowths. 

 Very similar cell inclusions appear in the cutaneous lesions of 

 variola, vaccine, and human molluscum contagiosum, and are re- 

 garded by some as the causative agents of the disease, it being 

 held that they are protozoan in character. Councilman (1904) 

 and his associates have especially emphasized these points, a life 

 cycle having been worked out for Cytorcytes variolae by Calkins 

 (1904). In the hope of being able to discover the nature of the 

 cell inclusions in epithelioma contagiosum we examined about 

 four hundred sections from the lesions appearing on the head 

 and on the mucous membranes of the mouth and throat. These 

 sections were taken at varying intervals, mostly from the third 

 to the twelfth day. They were fixed in Zenker's fluid and hard- 

 ened by the usual methods and stained by the following methods : 

 (1) hematoxylin and eosin ; (2) Giemsa 's blood stain ; (3) Heid- 

 enhain's iron haematoxylin and Bordeaux red; (4) Miihlens- 

 Hartmann's vaccine stain; (5) von Wasielewski 's stain; (6) 

 Mann's eosin-methylene blue; (7) Osmic acid; (8) Sharlach R; 

 and (9) Levaditi's silver impregnation method. Also a large 

 number of smears were made directly from the tumor growths, 

 fixed with methyl alcohol and stained by the Giemsa method. 



