Tuni.ors 313 



were fifteen cases in which tumors of similar nature occurred 

 in two or more organs. In these cases the tumor had prob- 

 ably iindergone metastasis. 



The age of the bird is also related to frequency of the 

 occurrence of tumors. Tumors being much more frequent 

 in old than in young birds. Only 7.37 per cent of the birds 

 under two and one-fourth years of age had tumors, while 

 19.17 per cent of those older than this were affected. 



A further proof of the common occurrence of new tissue 

 growths in fowls is the fact that in the course of ten months 

 Rous, Murphy, and Tytler ^ obtained without difficulty 

 about thirty spontaneous tumors in living fowls. 



Fowl tumors are apparently in every way analogous to 

 tumors in human beings. They are masses of new tissue 

 (neoplasms) which persist and grow independently of the 

 surrounding structures. These growths are of no physiolog- 

 ical use to the host but they are often harmless. Tumors 

 may be classified as malignant or benign. Benign tumors do 

 not penetrate into the surrounding tissues but push them 

 aside. They are usually encapsuled. On the other hand 

 there are a number of tumors which are malignant and tend 

 to infiltrate the tissues. Many of these produce growth in 

 adjacent organs and even in distantly removed parts of the 

 body. Usually they affect the general health and when 

 removed tend to recur. 



On examining four thousand hens brought to a hotel, 

 Ehrenreich^ found seven malignant tumors. All of these 

 were found in one thousand hens more than one year old. 



1 Rous, P., Murphy, J. B., and Tytler, W. H., " A Filterable Agent 

 the Cause of a Second Chicken Tumor, an Osteochondrosarcoma." 

 Jour. Amer. Med. Assoc, Vol. 59, pp. 1793-1799, 1912. 



2 Ehrenreieh, M., and Michaelis, L., "Ueber Tumoren bei Huh- 

 nern." Zeitschr. f. Krebsforch, p. 586, 1906. 



Ehrenreieh, M., "Weitere Mitteilungen iiber das Vorkommen 

 malignes Tumoren bei Huhnern." Med. Klin., BerUn, III, 614, 1907. 



