Cancer in Various Strains of Mice. 



35 



on the same farm. One of us described such observations in the 

 case of carcinoma of the inner canthus of the eye in cattle found in 

 increased number on a farm in Wyoming and in the case of three 

 sarcomata of the thyroid in a relatively small number of white 

 rats kept in a few cages in the laboratory of the Chicago Polyclinic 

 and compared this phenomenon to the so-called endemic occurrence 

 in man, but emphasized from the beginning that we had to consider 

 not only infectious, but also hereditary conditions as possible 

 causative factors. 



While in the case of certain cancers, for instance the squamous 

 cell carcinoma of rats observed by Hanau, the above mentioned 

 carcinoma in cattle and the sarcoma of thyroids of rats and some 

 other similar cases observed by Borrel and others the unusual 

 frequency of the reported cases in certain places could not be 

 doubted, the significance of similar observations concerning the 

 frequent occurrence of mammary cancer in mice were less clear, 

 inasmuch as mammary cancer of mice is found everywhere and 

 sufficient comparative statistics do not exist as yet as to the normal 

 incidence of cancer in various strains of mice. 1 Our investigations 

 were therefore concerned with the incidence of cancer among 

 various strains of mice kept in the same breeding establishment, 

 especially with the view to decide definitely whether or not a 

 hereditary factor was detectible in the occurrence of spontaneous 

 cancers in mice. 



The principal results of our investigations which, after a few 

 preliminary observations were begun more than three years ago, 

 and which we hope to be able to continue, may be summarized as 

 follows : 



I. Mice raised in the same breeding establishment, under the 

 same conditions of climate and feeding show a very different 

 incidence of cancer of the mammary gland among female mice 

 depending on the strain or family to which the mice belong. To 

 give a few examples: The strain designated "English," 66.9 per 

 cent.; "Carter," 35 per cent.; "No. 8," 30 per cent.; cream, 3^ 



1 The more or less frequent occurrence of mammary cancer in mice in certain 

 cages or breeding establishments had previously been reported among others by 

 Eberth and Spude, Borrel, Michaelis, Gaylord and Clowes (who also observed the 

 occurrence of sarcoma of rats in cages in which one of us had previously kept rat3 

 inoculated with sarcoma), Apolant, Ascher, Henke. 



