MICE: THEIR BREEDING AND REARING FOR 

 SCIENTIFIC PURPOSES 1 



DR. J. FRANK DANIEL 

 University of California 

 I. Introduction 

 Notwithstanding many shortcomings mice have con- 

 tributed much to the advancement of science and the serv- 

 ice of mankind. To realize this we have but to recall 

 that it was by crossing the white with the gray mouse 

 that Mendel's Law of Inheritance was first found to 

 apply to the animal kingdom (1) ; that from a study on 

 mice some of the earliest concepts of immunity were ob- 

 tained (2) ; and that from experiments now in progress 

 on them an insight is being gained into the nature of 

 cancer (3). These and similar experiments indicate 

 something of the scope to which these animals have been 

 put. 



The ease with which white mice can be handled makes 

 them, in many ways, preferable for experimentation to 

 other and larger rodents. But, owing to a widespread 

 notion that they are difficult to rear under laboratory 

 conditions, their usefulness has been greatly curtailed. 



The method usually employed in the breeding of mice 

 has been what we may term extensive. By this I mean 

 that many animals are kept from which to obtain off- 

 spring. I have set myself the task of breeding mice in- 

 tensively, that is, of keeping relatively few, but of keep- 

 ing these under conditions which will insure their pro- 

 ductivity. It is the purpose of this paper to describe the 

 way in which this was done. 



II. The Intensive Breeding of Mice 

 A. Detrimental Factors 



1. Marked Fluctuations in Temperature.— Probably 

 no single factor is more likely to be overlooked than that 

 mice, to produce to the best advantage, require an 

 equable temperature. While they can withstand extremes 



1 From the Zoological Laboratory, University of California. 



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