NEOPLASTIC DISEASES IN CHICKENS 49 



are too small to be regarded as a representative sample indicative of the true 

 condition for all chickens. In view of these facts, the results are suggestive only. 



The quarterly incidence for all tumors in birds examined varied from 10 to 

 15.9 percent, indicating little effect of season upon incidence of tumors. However, 

 when the seven types of tumor on which usable information was available were 

 considered, there was only one (myelocytoma) in which season seemed to have no 

 effect. Season or quarter of year seemed to have an irregular effect on the inci- 

 dence of other neoplasms. Thus the incidence of lymphocytoma was high in the 

 first and fourth quarters, leiomyoma high in third quarter, embryonal nephroma 

 high in the fourth quarter, leukosis high in the second quarter, epithelial tumors 

 high in the fourth quarter, and fibrosarcoma high in the second quarter. The 

 similarity of incidence b}' quarters in leukosis and fibrosarcoma is of interest, for 

 these two neoplasms were the only ones to show comparable rates of incidence. 



These findings cannot be regarded as conclusive and merely suggest the need 

 for further information. 



Distribution of Lesions 



The data on all cases of neoplasia were compiled to give information on two 

 items; namely, the frequency of involvement of organs and tissues and the 

 varieties of neoplasia found in different organs and tissues. These data are given 

 in Table 25. The greatest variety (nine different kinds) of tumors was found 

 in the musculature. The liver, gonad, and skin and subcutis each were affected 

 with eight varieties of tumor; and the kidney, peritoneum, and intestine with seven. 

 Six kinds of tumor were found in the lung and five in the heart. Four varieties 

 were found in the spleen, adrenal, and pancreas. Three varieties were found 

 affecting the blood, bone marrow, oviduct and its ligament, thymus, thyroid, 

 parathyroid, and nerve tissue. The relative frequency of involvement of organs 

 and tissues is indicated in Table 25 where they are listed in the descending order 

 of frequency of involvement. The large number of cases of lymphocytoma had 

 a marked effect on this arrangement since it was the most common type of tumor. 



The distribution of lesions in the collection of neoplasms provides material that 

 may be a useful guide in diagnosis. For example, the liver was the organ most 

 frequently affected with new growths and although eight varieties of neoplasia 

 were found, the most common type was lymphocytoma. This suggests that 

 a neoplastic process in the liver is quite apt to be lymphocytoma and the sug- 

 gestion can be tested b\- further consideration of the gross characteristics of the 

 process and involvement of other tissues and organs. A similar analysis may be 

 made with respect to other organs or tissues found affected with neoplasia. 

 Obviously, of course, such generalizatioas are subject to error; yet they provide 

 a basis for a rational method of arriving at a tentative diagnosis of a neoplasm 

 as discussed in the next section. 



Correlation between Tentative and Final Diagnoses 



In order to obtain information on the reliability of diagnoses of neoplasia 

 based only upon macroscopic examination, a plan to test this point was followed 

 during the collection of most of the cases included in the survey. A tentative 

 diagnosis was given each case at the time of necropsv- and this was later correlated 

 with the final diagnosis made after histological examination. 



The results of this phase of the study are given in Table 26. The principal 

 factors utilized in making the tentative diagnosis were the situation of the tumor 

 and the consistency, texture, color, general character, and distribution of the le- 

 sions. Such factors as age of the bird and length of illness were given minor con- 



