ABSTRACT
The ablation of the pituitary gland in the Axolotl larva of Amblystoma tigrinum at an age when the thyroid gland has developed does not produce any significant alteration in the growth rate when compared to the growth rate of the normal animal.
The researches of Cushing† and others indicate that the partial removal of the pituitary gland in the young mammal inhibits normal growth. In Amphibia, Smith (1920) and Allen (1917) have shown that the early ablation of the hypophysis anlage in frog embryos produces, in addition to the characteristic pigmentary disturbances consequent on pituitary removal : (1) failure to undergo metamorphosis ; (2) retardation in the development of the thyroid gland; (3) a diminished growth rate of the body as a whole.
It is not clear how far the third effect is independent of the undevelopment of the thyroid gland.
The object of the present communication is to record data concerning the growth in body weight of Salamander larvæ after the removal of the pituitary body subsequent to the development of the thyroid gland.
The material used for this experiment was the Axolotl larva of Amblystoma tigrinum, the European strain of which does not undergo metamorphosis if kept in aquaria.
The operations were performed by Dr Lancelot Hogben by the technique developed by him, and described in a previous issue of this Journal.
In all, thirteen individuals were operated on, their ages ranging from six months to one year. A corresponding series of controls of similar age was used. The animals were kept singly in jars of water, and were weighed fortnightly for a period of eighteen weeks subsequent to the operation. For the first seven weeks the animals (operated and controls) were fed three times a week on raw beef, and subsequently the animals were fed daily on fresh ox liver for the duration of the experiment. This change of diet was suggested by experimental feeding of Salamanders by Uhlenhuth, who found that ox liver favourably influenced the rate of growth.
The experimental series displayed no evident disturbance as the result of the removal of the gland apart from the characteristic pallor described by Hogben. This was maintained throughout the course of the experiment. Two animals of the operated series died, in one case through mis-adventure owing to breakage of the container. They showed no signs of œdema. The remainder took their food readily, and there seems no reason to doubt that in Salamander larvæas in Anuran tadpoles, the removal of the gland in no way impairs the normal viability of the animal.
The observations on the growth rate are set forth in the accompanying tables and chart (pp. 76, 77).
From these it will be seen that increase in body weight took place in both series. The growth rate as measured by the weight ratio in the two series is higher in the controls, but a high degree of significance does not atatch to this difference seeing that it is only about two and a half times its probable error.
As, however, inspection of the graph reveals, the main falling off in the growth rate of the hypophysectomised animals was towards the end of the experiment, when the effects of operation could not possibly contribute to the result.
References
Dott, N. M. (1923), “An Investigation into the Functions of the Pituitary and Thyroid Glands,” Quart. Journ. Exp. Physiol., 18, Nos. 3, 4.