30 University of California Publications in Zoology [Vol. 11 



Scientific Importance. — In addition to its economic signific- 

 ance, epithelioma eontagiosum is a disease of unusual scientific 

 interest, not only because of the obscure nature of its etiology, 

 but because of its apparent relationship or resemblance to other 

 diseases. Because of the epithelial hyperplasia, which is one of 

 the most striking feavures of the disease, there has been a ten- 

 dency to classify the lesions produced as neoplasms. Because of 

 the presence of a filterable virus and cell inclusions resembling 

 those of human molluscum eontagiosum, variola and vaccinia, 

 it has been classified as one of the exanthemata, and its exciting 

 agent reputed to be a protozoan, in common with many other 

 diseases of this class. Again many others as Priedberger and 

 Frohner (1908), Schmid (1909), Sigwart (1910), and Kinsley 

 (1907) assert that epithelioma eontagiosum and avain diphtheria 

 are different manifestations of the same disease, varying only in 

 clinical features and in nature of, or severity of infection with 

 the same causative agent. This latter contention is based on the 

 fact that in many cases fowls present the clinical features of both 

 diseases simultaneously, and that by inoculation with material 

 taken from chickens having apparently one disease, both diseases 

 may be produced. 



With the hope of throwing some further light on the cause 

 and nature of this most interesting disease, the following study 

 was attempted. It is necessarily incomplete and leaves many 

 points requiring further investigation. However, perhaps others 

 may be led to give their attention to further studies of this 

 disease, because of some of the data here presented. The in- 

 vestigations here reported were carried on under a grant from 

 the Federal Adams fund, of the Agricultural Experiment Station 

 of the University of California, for which grateful acknowledge- 

 ments are here made. The work has been under the direction 

 of Professor Charles A. Kofoid, of the Department of Zoology, 

 and Assistant Professor Clarence M. Haring, of the Veterinary 

 Division of the Agricultural Department, for whose many sug- 

 gestions and criticisms I am deeply indebted. I should also like 

 to aelcnowledge the kindly interest shown by Assistant Professor 

 G. Y. Rusk, of the Department of Pathology, and the continual 



