THE ADRENAL GLANDS 91 



The tadpole as a reagent to test out the growth effects of differ- 

 ent glands of internal secretion has also been employed for the 

 pineal. Ten-day-old tadpoles fed on pineal present a marked 

 translucency of the skin due to a retraction of the skin pigment 

 cells. Now without a doubt a number of as yet unknown growth 

 and metabolic effects follow exposure of the body to the complete 

 gamut of light rays. The interesting suggestion follows that the 

 pineal influences the body by varying the degree of light ray 

 reaction. 



The pineal, the ghost of a once important third eye at the 

 back of our heads, still harks back in its function to a regulation 

 of our susceptibility to light, and its effect upon sex and brain. 

 So it becomes one of the significant regulators of development, 

 with an indirect hastening or retardation of puberty and maturity 

 according as it works in excess, or too indolently. It appears 

 thus the blood brother of the adrenal cortex which also influences 

 the skin pigment and so susceptibility of the organism to light, 

 brain growth and sex ripening. It is interesting that Descartes, 

 in 1628; considered the pineal the seat of the soul. 



The Parathyroids 



Sometimes imbedded within the substance of the thyroid in the 

 neck, sometimes placed directly behind it upon the windpipe, 

 are four tiny glands, each about the size of a wheat seed, 

 the parathyroids. For long they were swamped in the nearness 

 of their great neighbor, and considered merely a variable part of 

 it. There are some who contend that even today. But it has 

 been proven that they are separate, individual glands, with a 

 structure and function of their own, and a definite importance 

 to the body economy. 



On the animal family tree they appear early, contempora- 

 neously with the thyroids. In the embryo they develop from 

 about the same sites. And very often they look very much alike 

 under the microscope, especially when the cells are in certain 

 quiescent stage of secretion. Yet they are wholly independent in 

 nature, activity and business. 



First experimenters upon the effects of removal of the thyroid 

 were confused by contradictory findings with different animals 

 because in some they would take out the parathyroids at the 

 same time without knowing it, and in others they would not. 

 That possibility suggested, more careful dissectors accomplished 



