540 EPITHEI.IOMA CONTAGIOSUM 



lated to small pox. Spinola failed to produce it in fowls with 

 cow pox. In 1873, Bollinger gave a very full account of his 

 investigations into its nature. 



§ 428. Geographical distribution. This affection has 

 been studied in Europe. In the United States, Salmon refers 



Fig. 121. A photograph of the head of a fowl shoicing epithelioma on 

 the comb and in front of the eye {after Ward). 



to it from the Southern States and Ward has described it in 

 California. Sedgwick reports that it is one of the greatest 

 obstacles to chicken raising in Hawaii. 



§ 429. Etiology. The cause of this disease is not satis- 

 factorily settled. Rivolta and Silvestri considered coccidia to 



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