Abstract
In former experiments on the effects of the injection of acid extract of cattle anterior pituitary on the thyroid gland of guinea pigs, we had found indications that these effects did not increase with continued injections. To determine the effects of long continued administration, a considerable number of young guinea pigs were given daily injections of anterior pituitary extract over a long period of time. Excluding those animals which were examined within the first 6 weeks after the beginning of the experiment, 10 guinea pigs received injections during a period of time varying between 47 and 74 days. The individual amounts injected daily varied between 1 cc. and 3 cc. of the extract. In some cases a few initial doses of 1/2 cc. were given. The total amounts injected ranged between 47 and 135 cc. The initial weights of the individual guinea pigs were between 185 and 205 gm. except one animal weighing 230 gm. There was a great difference between the weights reached at the end of the experiment. Some animals had gained considerably, while others remained unchanged.
The microscopic examination of the organs showed that the severity of the effects of extract did not correspond to the amount injected. The animals evidently varied greatly in resistance. The resistant animals showed the least changes in their organs and these gained most rapidly in weight, while the most susceptible ones showed the greatest changes in their thyroid and sex organs, and did not gain as much or as rapidly in weight as the others. The former group became most readily adapted even to increasing doses of the extract. Thus those animals receiving the largest daily doses gained most in weight and their thyroid and sex organs showed the least change from normal or no change at all.
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