GROWTH AFFECTED BY FEEDING DUCTLESS GLANDS 305 

 IV. ORIGINAL OBSERVATIONS 

 1 . Body as a whole {weight and length) 



a. Comparison of controls with norms. The growth of the 

 younger groups of rats, especially the males, in this investiga- 

 tion varied considerably from that of the rats described by most 

 of the previous workers for rats collected at random from a 

 colony. It is necessary therefore to make a comparison of the 

 animals with the norms of other investigators before discussing 

 the effects of the ductless gland feeding. In this comparison, 

 only the control rats will be considered directly. With the 

 exception of certain data of the thyroid-fed groups which will 

 be discussed later, however, there is a close agreement among 

 the corresponding data of all the groups so that the data of the 

 control animals represent indirectly most of the data of the 

 entire series. 



A great difference between my rats (especially the 'younger' 

 or 'winter-born' males) and those previously described by Don- 

 aldson and Jackson is to be noticed in the rate of growth both of 

 body length and of body weight. The albino rats described by 

 Donaldson ('06) and by Jackson ('13 and '15) of different strain 

 and different diet are considerably hghter in weight than are mine 

 at corresponding ages, up to the fourth month. (See table 1 

 and charts 1 and 2). The selected 'strong and vigorous' Utters 

 described by King ('15), however, correspond rather closely 

 with mine in body weight. 



The rate of growth varies thus in albino rats from different 

 sources, depending partly upon the 'strain,' but more upon 

 diet and general environment. King's results indicate also 

 that a more rapid growth may be expected from those litters 

 in which at birth the individuals are especially large and strong. 

 The vigorous average growth of my rats appears chiefly in those 

 designated as the 'younger' ('winter-born') Utters. The growth 

 of the 'older' ('summer-born') animals throughout is more 

 nearly Uke that found by Donaldson and Jackson (charts 1 and 2 ; 

 table 1). As the 'younger' group had been eliminated largely 

 at 110 (and partly at 70) days, the final averages are relatively 



