The Endocrine Glands - 399 



ternally; and there are some organs, such as 

 the stomach, intestine, and perhaps the kid- 

 ney, which produce hormones as a minor, or 

 incidental, sideline to their regular activity 

 (p. 307). 



METHODS OF ENDOCRINE RESEARCH 



Deficiency and replacement experiments 

 are widely used in endocrinology. If a gland 

 is removed from an animal, and the animal 

 develops drastic dysfunctions as a result of 

 the deficiency, there is no justification for 

 believing that the excised organ is an endo- 

 crine gland — unless the impaired functions 

 can be restored by replacing the gland, either 

 by grafting it in another part of the body or 

 by injecting extracts prepared from the ex- 

 cised tissue. Replacement by glandular ex- 

 tracts is a particularly valuable technique, 

 because the method of extraction provides a 

 good index of the chemical nature of the 

 hormone and ultimately may lead to the 

 isolation, identification, and synthesis of the 

 active compound. Moreover, if more than 

 one hormone is present in the excised gland, 

 these hormones can be separated by prepar- 

 ing different extracts. In this way, for exam- 

 ple, several distinct hormones have been 

 obtained from the pituitary gland; and each 

 separate hormone restores some but not all 

 of the dysfunctions associated with the re- 

 moval of the whole pituitary gland. 



Overdosage methods are also quite useful 

 in endocrinology. Grafting extra gland tis- 

 sue, or injecting extracts— without first re- 

 moving the gland in question — may give 

 symptoms more or less opposite to the de- 

 ficiency effects; in clinical cases, hyperactivity 

 of a diseased gland may provide some clue 

 as to the normal functions. 



In the final analysis, however, a hormone 

 is not established until it has been isolated 

 and identified as a pure substance. In recent 

 years this goal has been reached in the case 

 of almost all of the principal hormones (see 

 below). Moreover, many of these compounds 

 have now been artificially synthesized. 



THE TESTIS AS AN ENDOCRINE GLAND 



In addition to its sperm-forming function, 

 the testis produces testosterone, a very active 

 hormone that stimulates the development 

 of the secondary sexual characteristics of 

 maleness in all vertebrate species. 



The drastic results of castration, over and 

 above the mere development of sterility, have 

 been recognized since ancient times, and 

 several classical accounts describe the charac- 

 teristics of the eunuch, especially emphasiz- 

 ing the high-pitched voice, the hairless face, 

 obesity, and mental inertia. In fact, several 

 ancient peoples resorted to castration, em- 

 ploying the eunuchs as safe keepers of the 

 harem. 



The castration of any vertebrate tends to 

 suppress the secondary sexual characteristics 

 of the species. The capon, for example, lacks 

 the large comb of the cock, and the body of 

 a capon becomes unusually plump. The 

 gelding also becomes heavier and more docile 

 than the stallion, and hence the gelding is 

 more usefid as a beast of burden. 



The secondary characteristics of the male 

 can be restored to the castrate by grafting or 

 injecting testicular material, and this fact 

 provided the first evidence that the testis is 

 an endocrine gland. In the capon, for exam- 

 ple, the characteristics of the cock — aside 

 from fertility — can be restored by a suitable 

 regime of testicular injections; in fact even 

 a young hen will take on the bodily features 

 and habits of a rooster if subjected to a 

 similar treatment. 



Testosterone is produced by the inter- 

 stitial tissue of the testis, which occupies the 

 space between the sperm-forming tubules (p. 

 385). This fact was first suspected from clini- 

 cal evidence. In cases of cryptorchy (p. 383), 

 the undescended testis displays an almost 

 normal amount of interstitial tissue, but the 

 sperm-forming tubules are degenerate. Thus 

 a bilateral cryptorchicl, although completely 

 sterile, largely retains the secondary attri- 

 butes of masculinity. The temperature in 

 the abdominal cavity is higher than in the 



