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C. M. JACKSON 



Fig. 1 Photograph showing four albino rats at the age of ten weeks. The 

 larger rats represent the normal, full-fed controls. The smaller rats are from 

 the same litter, but have been held by underfeeding at constant body-weight 

 since the age of three weeks. The rats are pure albinos (Mus norvegicus albinus) 

 the dark spot on the head of one being an artificial mark of identification. 



slant body-weight for varying periods, from the age of three 

 weeks up to the age of six weeks (8 rats) to eight weeks (3), to 

 ten weeks (22), to thirteen weeks (1) and to sixteen weeks (1). 

 A few were hekl at constant body-weight beginning at later 

 periods, — from age of six weeks to age of thirty-two weeks (2), 

 and from age of ten weeks to age of thirty-six weeks (3). Con- 

 trols (25 in all) were also killed at the beginning and at the end 

 of these time periods. At ten weeks of age, the normal controls 

 are half-grown rats, sexually mature, of nearly adult proportions. 



