THE RAT 



INTRODUCTION 



The Norway rat, Mus norvegicus, is the one mammal now 

 easily obtainable both wild and as a domesticated form. This 

 latter is represented by either the Albino or the pied rats so com- 

 mon in our laboratories. 



The Albinos are clean, gentle, easily kept and bred, and not 

 expensive to maintain. They are omnivorous, thriving best on 

 table scraps. The span of life is about three years and breeding 

 begins at about three months. Furthermore the species is cos- 

 mopolitan. The Utters are large and may be had at any sea- 

 son. The young are immature at birth. The domesticated 

 Albino crosses readily with the wild Norway. The rat, both wild 

 and domesticated, takes exercise voluntarily and is susceptible 

 to training. It is also highly resistant to the usual wound- 

 infecting organisms. For a number of lines of study therefore, 

 the rat seems to be a peculiarly suitable animal. 



Through the researches of several investigators at The Wistar 

 Institute (since 1906) and through those of E. H. Dunn and of 

 J. B. Watson at the University of Chicago, of Chalmers Watson 

 and Sir Edward Schafer at Edinburgh, of C. M. Jackson and 

 L. G. Lowrey at the University of Missouri, of J. R. Slonaker 

 at Leland Stanford University, of T. H. Osborne and L. B. Mendel 

 at Yale University, of E. V. McCollum at the University of 

 Wisconsin, as well as through those of several other investigators 

 both in this country and abroad, there has been gathered a con- 

 siderable body of data applying to the weight and size of the do- 

 mesticated albino rat and its parts, as well as some similar data 

 applying to the wild Norway rat, the parent species. It is the 

 body of facts so gathered that it is our purpose to present, as 

 far as possible in tabular form. 



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