NEOPLASTIC DISEASES IN CHICKENS 47 



substantiated b}' the present study. Gass (11) as well as others had prev^iously 

 noted the tendency for epithelial tumors to be found in birds over one year of age. 



The small number of cases of other varieties of neoplasia does not permit definite 

 conclusions on the subject of age. However, nearly all of the other types were 

 found in birds less than one year of age. 



Sex 



Tumor incidence becomes quite difficult to correlate with the factor of sex for 

 several reasons. Although approximately equal numbers of male and female 

 chickens are obtained at the time of hatching, a variety of conditions immediately 

 enter to cause a change of the 1:1 ratio. Some commercial hatcheries separate 

 the chicks into male and female groups immediately upon hatching and may sell 

 either according to dem.ands of the buyer. Some poultrymen raise only males, 

 which are disposed of as broilers at a comparatively early age. Others raise only 

 females, which are held for varying periods in egg-producing flocks. Still other 

 poultrymen raise both males and females to broiler age or to sexual maturity 

 (4 to 6 months). The flock may then be reduced to a point where only a rela- 

 tively few males are retained for breeding purposes. The ratio of males to females 

 may vary greatly in such flocks from 1:4 to 1:10. These factors and probably 

 others influenced the relative numbers of males and females e.xamined in the 

 laboratory and in turn would influence the results obtained in the survey. While 

 a ratio of 1 male to 4.8 females may be calculated for all birds examined in the 

 laboratory, the ratio varied markedly (from 1:1.4 to 1:14) in the dift'erent age 

 groups (calculated from data in Table 21). 



Despite these diflficulties some conclusions seem warranted from examination 

 of the data on sex in Table 22. Leiomyoma was found only in females,- and 

 epithelioblastoma was found 16 times in females and only once in a male, strongly 

 suggesting a tendency for these diseases to occur principally in females. Both 

 tumors were often found in female reproductive organs and the preponderance of 

 females with these tumors was, therefore, not surprising. 



Embryonal nephroma was found relativeh" more often in males (6 cases) than 

 in females (8 cases). The sex ratio of 1 male to 1.3 females for this tumor may be 

 compared to the ratio of 1:4.8 among birds e.xamined whose ages were from 2 

 to 12 months (272 males and 1293 females, Table 21). Such a comparison is 

 logical, for such tumors were found in birds of this age group (Table 22). 



The sex ratios in m3'eloc\toma, leukosis, and fibrosarcoma were not greatly/ 

 different from that of all birds examined in the comparable age group. 



The question of sex in relation to lymphocytoma presents a problem in analysis. 

 Most investigators commenting on the subject have stated that lymphocytoma 

 appears as often in males as in females when the relative number of each sex in the 

 general poultry population is taken into account. A similar conclusion could be 

 drawn from the present study if one considered only the entire group of 213 

 cases among which were 20 males and 193 females, a ratio of 1 :9.7. This ratio of 

 approximately 1:10 is perhaps not greatly dissimilar from what might be ex- 

 pected to exist in the population of many general poultr\' farms. However, the 

 question cannot be dismissed so lightly, for among 148 cases of lymphocytoma 

 in collections A and B only 5 males were found with the disease as compared to 

 143 females, a ratio of 1 :29. No such disproportionate ratio existed in any of 

 the age groups of birds examined (Table 21). This was indeed a surprising result. 

 Although the number of males e.xamined (328) was small, 30 cases of lympho- 

 cytoma should have been found among males if the rate of 9.1 percent incidence 

 for females (143 cases among 1575 examined) could be applied to males. The low 

 rate of incidence for males in collections A and B indicates the need for careful 

 analysis. For example, the addition of cases from collection C completely changed 



