24 MASS. EXPERIMENT STATION BULLETIN 391 



12 to 79 weeks with an average of 42,0. Thirteen of the birds were females and 

 three were males. 



Data on egg production were available for only one bird, case T 44. This bird 

 laid 168 eggs during a production period of 328 days. The production index of 

 0.512 was only slightly lower than the average (0.534) for the flock from which 

 the bird came. The last egg was laid only 41 da\'s before the bird died. 



Osteochondrosarcoma 



Only one example ot osteochondrosarcoma was found. This developed on the 

 skull, dorsal and posterior to the external canthus of the left e\e. 



1. Case T 234. The owner had noted a swelling on the head of the hen and 

 submitted it for examination at the age of 5 months. The tumor did not seem to 

 discommode the bird. The mass measured approximatel)' 3X 2.5 X 2 cm. It 

 was firmly attached to the bone of the skull and on cross section many small yellow 

 bony foci were found scattered throughout the substance of the tumor. The 

 major portion of the tumor was faintly blue-gray in color and had a glassy ap- 

 pearance. Microscopically the tumor was composed principally of immature 

 chondroblasts which had produced much intercellular chondromucin. There were 

 scattered areas in which the chondroblasts assumed a more adult form resembling 

 cartilage cells, and in these areas were deposits of calcareous material indicating 

 the formation of bone (Plate VII, Figure 3). The liver, spleen, and bone marrow 

 of the femur were found to be negative for pathology upon both gross and his- 

 tological exmaination. 



Fibrochondrosarcoma 



Only one case of fibrochondrosarcoma was encountered. 



1. Case S 2630. This tumor was found in the subcutis of the back, in the 

 pectoral muscle, in muscles of the thigh, and in the tendinous, aponeurotic at- 

 tachments of muscles to the sacrum and patella of a year-and-a-half-old hen 

 that was killed for examination. The visceral organs and the bone marrow were 

 essentially negative for pathology. The cellular morphology of the tumor was 

 somewhat variable in different areas. In genera! it was a mixture of immature 

 fibrcblast-like cells and immature, neoplastic cartilaginous cells. The latter type 

 of cell was usually predominant. The cartilaginous cells were more or less closely 

 related in a syncitial arrangement. The nuclei were sometimes double and in 

 differentiated areas quite similar to those of adult cartilage cells. The cytoplasm 

 of the cells was a slate-blue color with hematoxylin and eosin stain and as men- 

 tioned above the cell borders were sometimes indistinct. The fibroblast-like 

 cells were spindle-shaped with faintly blue staining cytoplasm and had relatively 

 large vesicular nuclei. Transitional forms between the two types of cells were 

 apparent. 



The primary site or point of origin of the tumor could not be determined. The 

 tumor of the subcutis manifested itself as areas of thickening of the skin, one of 

 the largest of which measured 35 mm. in diameter. The tumor tissue was gray 

 in color, very firm and fibrous. In the muscles, the tumor had a similar color 

 and appearance and tended to infiltrate and destro>' the muscle tissue. 



From the data on egg production by this bird a production index of 0.463 was 

 calculated (93 eggs in 201 days of productive life). The last egg was laid 247 

 days previous to necrops}-. 



Histiocytic Sarcoma 



The term histiocytic sarcoma has been introduced by Jackson (13) to include 

 those tumors which take their origin from the histiocyte. The diagnosis of 

 histiocytic sarcoma lequires careful microscopic study of the complex structure of 

 such tumors. Neoplastic histiocytes may assume the form of macrophages, 

 fixed stellate cells, and fibroblasts, in addition to intermediary forms between 

 these cell types. Usually all forms of neoplastic histiocytes may be found to a 

 variable extent in different parts of a typical histiocytic sarcoma. 



