Tumors 315 



I. Connective tissue type. 



II. Epithelial tissue type. 



III. Muscle tissue type. 



IV. Nervous tissue type. 



Each of these groups may be subdivided according to the 

 more specific resemblance of the histology of the tumors to a 

 particular kind of body tissue. At least six different types 

 of the first group have been described in the domestic fowl. 



I. Tumors of the connective tissue type. 



1. Sarcoma (made up of embryonic connective tissue 

 composed of closely packed cells embedded in a fibrillar or 

 homogeneous substance). 



2. Myxoma (mucous tissue, a soft translucent growth, made 

 up of variously shaped cells of connective tissue and capillary 

 blood vessels incased in a jelly-like matrix. 



3. Fibroma (composed mainly of fibrous or fully developed 

 connective tissue). The tumors of this group are benign. 



4. Chondroma (a cartilaginous growth). 



5. Osteoma (bony tissue usually but not always develop- 

 ing on bone). 



6. Lymphoma (made up of lymphoid tissue). 

 According to Tyzzer and Ordway ^ tumors of the sixth 



group (lymphomata) occur more frequently than any other 

 type. They suggest that this is probably due to two facts. 

 (1) This type of tumor apparently develops in younger birds 

 than other types, and (2) birds kept for egg production are 

 usually killed at the end of their first year. They have 

 described in detail seven different tumors of this group. In 

 summing up their results they say : " In some cases lymph- 

 oma occurs as a local primary growth either with or without 

 metastasis. In other cases the tumor tissue is so uniformly 

 disseminated throughout certain organs that it is impossible 



'Tyzzer, E. E., and Ordway, T. "Tumors in the Common 

 Fowl." Jour. Med. Research, Vol. 21, pp. 459-477, 1909. 



