Abstract
The mitotic activity of the thyroid gland in the guinea pig can be used as a quantitative measure of the stimulating effect exerted by various agencies on this organ. 1 In the following investigations we extended this method to the adrenal gland of the guinea pig and we determined the number of mitoses in this gland in the normal animal and under various experimental conditions. We soon found that there is a remarkable similarity in the mitotic activity in various sections through this organ at the same time, so that it is possible to obtain the measure of the mitotic activity of a gland by counting the mitoses found in 3 longitudinal sections through the center of this organ, each section being approximately 6 mikra thick. Counting the number of mitoses in a larger number of sections does not cause a significant alteration in the figures. The large majority of all mitoses are found either in the zona glomerulosa or in the outer portion of the zona fasicularis and it seems that, in the former area, mitoses occur especially in younger individuals. In these investigations, we excluded all animals which showed any sign of infection. In normal guinea pigs weighing 190-200 gm. the average number of mitoses per section is about 5; this number declines with increasing weight and age. In guinea pigs weighing 400-600 gm. it is about 1.5 mitoses per section. This series of normal animals includes 87 cases. There is no appreciable difference between males and females. The total number of mitoses in one adrenal gland of a guinea pig weighing 195 gm. was 1340, in the adrenal gland of a guinea pig weighing 340 gm., 930, and in a guinea pig weighing 515 gm., 165. Canalis stated that in sections of suprarenals from normal guinea pigs there might be 5 mitoses, in others as many as 12 per section. 2 Hoerr states that in sections cut 3 to 4μ one may expect to find on the average 2 to 8 mitoses in a longitudinal section through the center of a gland of a young adult guinea pig (350-450 gm.). 3
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