CHAPTER LXXXVIII 

 THE PINEAL GLAND, THE GONADS, AND THE THYMUS 



THE PINEAL GLAND 



This peculiar structure lies between the anterior corpora quadrigem- 

 ina, and weighs about two-tenths of a gram. It is largest in the early 

 years of life, and undergoes retrogressive changes after puberty. Micro- 

 scopically it consists of epithelial cells arranged loosely in trabeculae, 

 with large sinus-like capillaries between them; neuroglia and sometimes 

 muscle-fiber cells are also present. Curious globules of calcareous mat- 

 ter (brain-sand) are also found, especially in the pineal gland of man. 

 The gland is developed from an evagination of the third ventricle, and 

 it is homologous with the so-called median eye of reptiles. 



The functions of the pineal gland are obscure. In cases where its 

 extirpation has been successfully accomplished (in the fowl), it has been 

 found that the body growth is stimulated and that the sexual characteris- 

 tics develop more quickly. This result would seem to indicate that the 

 clinical observation that tumors of the pineal gland associated in 

 young boys with abnormal growth of the skeleton and with early 

 development of the secondary sexual characteristics, depends on the 

 fact that a new growth produces destruction of the gland with consequent 

 hypopinealism. The immediate effects of the injection of extract of pineal 

 gland are not characteristic, consisting merely of a fall in blood pressure, 

 which is, however, obtainable when an extract of practically any cellular 

 organ is injected. Prolonged administration of an extract to growing ani- 

 mals is said to accelerate the growth and to bring about a precocious develop- 

 ment of the sexual organs; but this result is somewhat difficult to inter- 

 pret, for, as we have just seen, similar changes occur after experimental 

 removal of the gland. It is stated by McCord and Allen 56 that the pig- 

 ment cells (melanophores) of tadpoles become contracted after pineal 

 feeding. As the receptors of the reflex governing such color reactions of 

 various animals are situated in the retina, these investigators give signi- 

 ficance to their observations by correlating them with the fact that the 

 pineal gland, as stated above, is the representation of a reptilian eye. 



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