Distribution of erythrocytes with chromium 51 was used to compare the capillary volume of adipose tissue and resting skeletal muscle of rats. Based on wet weight, the vascular bed of adipose tissue is of the same order of magnitude as that of muscle, whereas the protein content of the muscle is approximately 16 times greater. The size of the vascular bed per gram of adipose and muscle tissues decreased considerably during aging.

Gonadal and perirenal fat pads from markedly obese mice show pathological changes associated with the appearance of many large macrophages, small mononuclear cells resembling lymphocytes, and polymorphonuclear cells. The first recognizable changes are always associated with necrosis of the fat cell membrane. Advanced stages also show reduction of the number of fat cells, formation of large fat vacuoles and cysts, and predominance of innumerable pathological cells. The extent of tissue changes varies considerably even within one fat pad but is dependent on the degree and duration of obesity. Animals weighing less than 45 gm are only occasionally, heavier mice almost regularly, affected. The nitrogen content of normally healthy adipose tissue decreases as the animals grow older and fatter, while fat pads exhibiting tissue pathology show the expected increase in the protein and water content, and a reduction of the lipid content. The pathological changes were observed

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Male Wister rats weighing 240 ± 2 gm show an average protein and fat content of 41.6 gm, and 13.1 gm. During a period of normal growth, the body weight increases within 14 days to 311 gm, the protein content to 57 gm, and the fat content to 21.7 gm. Several groups of rats were subjected to experimental procedures for 14 days, after having reached a body weight of 240 gm. Administration of protamine zine insulin (12 u/day) greatly enhanced weight gain, and deposition of excess fat, without affecting accumulation of body protein. Cortisone (5 mg/day) produced variable results. Diminished gain of body weight and total body protein occurred in 60% of the animals while accumulation of body fat was normal. Some rats lost weight and body protein but comparatively less fat than animals losing fat due to food restriction. Weight loss was most frequently observed in rats with visible infections. Simultaneous administration of insulin (12 u/day) did not alter the cortisone effect on body protein but markedly increased accumulation of body fat. One hundred twenty units per day accelerated gain of body fat still more. Values were observed comparable to those found in rats receiving insulin only. The amount of total body fat closely paralleled the amount of adipose tissue the composition of which was not significantly altered by any of the hormonal manipulations.