BIRTH WEIGHT 



27 



ically separated from the mother at birth. Rats so obtained 

 are strictly new-born, while most rats designated as new-born 

 have suckled, as indicated by a white patch marking the 

 stomach. 



As the result of feeding unbalanced rations to rats Zuntz 

 ('19) concludes that both the number of litters and the num- 



TABLE 7 



Showing the birth weight data for 85 litters of stock and inbred albino rats arranged 

 according to the age of the mothers at the time that liters were cast 



TABLE 8 



Showing the birth weight data for stock and inbred albino rats arranged according 

 to the body weight of the mothers at the time that the litters were cast 



ber in the litter are reduced, but that the young which are 

 born tend to have both normal body weight and normal com- 

 position. 



7. Sex ratio. At the two periods of greatest reproductive 

 activity in the spring (March-May) and again in the autumn 

 (September-November) the proportion of males (the sex ratio) 

 is low. 



