Abstract
By ordinary two-dimension graphs, relationship between age and body weight in rats is well illustrated as well as relationship between various organs and age or body weight. Only by three dimension graphs however is it possible to illustrate the interrelation of age and body weight and also the weight of any given organ. 1 Such graphs have been particularly helpful in evaluating the influence of thymus extract on the various endocrine organs of the rat, whose general body growth is so much more rapid than normal. Thus it affords comparison with age-weight controls, in contrast to controls of comparable age but lower body weight or comparable weight and greater age. Eight thymus-injected rats exhibiting average precocity are used to illustrate the usefulness of these graphs.
Thymus-treated rats appear grossly normal, differing mainly in their size with respect to age. Therefore the “age-weight” graph of the injected rats is not parallel to the normal (Chart 1), nor is the “age-gland-weight,” since the thymus gland in thymus-treated rats is consistently heavier than normal. This increase in size is apparently due, on histologic examination, to the cortex being slightly wider than normal and less sharply demarcated from the medulla, both being crowded with lymphocytes. Hassall's corpuscles are less easily distinguished, seem fewer and are composed of fewer reticular cells than normal controls.
We gain the impression, through sacrificing rats and weighing the adrenals, that they tend to be below normal; plotted three dimensionally however (Chart 2) this does not seem to hold, nor was any deviation from normal observed histologically in the ordinary stains. (The graph for normal adrenals is the average between males and females for the plotted age-weight).
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