100 CM. JACKSON 



remains constant, the weights of the individual organs and 

 parts might also remain constant. (2) Since the normal growth 

 rates are known to vary in the different organs and parts, one 

 might expect those organs with the strongest normal growth 

 tendency to increase in weight at the expense of the remainder 

 of the body. (3) Since, however, the food-supply available is 

 insufficient for both maintenance and growth, the animals are 

 actually in a condition of chronic inanition; and changes might 

 be expected to occur corresponding to those which have been 

 observed in adults during inanition. 



A few observations have been recorded upon changes in 

 young animals in certain organs under these conditions, notably 

 by Waters ('08), Aron ('11 and '14) and Donaldson ('11). A 

 more extended and complete analysis of the changes in the 

 organism under these conditions seemed highly desirable, and 

 therefore the present investigation was undertaken. The work 

 was begun at the University of Missouri, and continued at 

 the University of Minnesota with the aid of a special grant from 

 the research fund of the Graduate School. This grant was used 

 to employ a research assistant, who cared for the animals and 

 assisted in the dissections, weighings, calculations, etc. An 

 abstract of the present paper has been published (Jackson '15 b). 



MATERIAL AND METHODS 



The albino rat (Mus norvegicus albinus) was chosen for use 

 in this experiment. It is a convenient animal on account of its 

 comparatively small size, rapid growth and hardiness under 

 experimental conditions. It is also practically the only mammal 

 whose growth norm (including variability) for the whole body 

 and for the various parts, systems and organs throughout the 

 post-natal life cycle is even approximately known. The effects 

 of inanition upon the adult rat have also been worked out (Jack- 

 son '15 a, '15 c) and are valuable for comparison. 



The material used in the present experiment included ten 

 litters (and one individual from an eleventh litter) as shown in 

 table 1. 



