Chap. 15 CHEMICAL REGULATION ENDOCRINE GLANDS 259 



endocrine glands are located in relatively similar positions in all vertebrates 

 (Fig. 15.1). 



Endocrine Glands 



Nomenclature. Endocrinology is a recent and very important study in which 

 many investigators have joined. New discoveries have suggested new names 

 until each gland and hormone has been christened and rechristened with sev- 

 eral names. The International Commission on Anatomical Nomenclature is 

 attempting to clarify this situation. 



Study of the Endocrines — An Illustration of the Experimental Method. 

 Endocrinology stands forth among biological subjects as a peculiarly striking 

 example of the successful use of the experimental method of study. The only 

 way to find out what a gland does is to show what occurs when it is removed, 

 thus creating a deficiency of its hormone, or what happens if it is implanted 

 into the body of a healthy animal, or its secretion or an extract is injected thus 

 creating an excess of the hormone. Thousands of experiments have been done. 

 In the pioneer days of endocrinology Charles Berthold made the first experi- 

 mental demonstration of the chemical effects of one part of the vertebrate body 

 upon another. In 1849 he removed the testes from young cocks and replanting 

 them, found that the usual changes after castration did not occur. In 1855 

 Claude Bernard put forth the idea that organs liberate special substances into 

 the tissue fluids and coined the phrase "internal secretion." Before these 

 experiments were made, there was only a vague knowledge of chemical con- 

 trol. Although much is still to be learned about endocrines, many of their 

 extraordinarily complex relationships have been clearly demonstrated. 



Light has been thrown upon the body at work by experimental surgery upon 

 living animals, especially by removing and transplanting glands. This has been 

 done with great care for the comfort of the animals, and the results have 

 proved highly important contributions to the intelligent treatment of human 

 diseases. That those who have "sugar diabetes" can live out their lives so suc- 

 cessfully is wholly due to experiments upon the pancreas of living animals. 

 Goiter, a serious disease of the thyroid gland, has been eliminated in many 

 regions thanks to the results first gained from the experimental treatment of 

 the goiter of fishes (Fig. 15.4). Other experiments include the culture of gland 

 cells outside the body under conditions which allow them to grow and to be 

 examined alive under the microscope. 



Thyroid Gland 



Form and General Activity. From the lower fishes to man, all vertebrates 

 have a thyroid gland. The human thyroid consists of a pair of lobes, one on 

 each side of the trachea joined by a band that crosses the trachea just below 

 the larynx (Fig. 15.1). It is supplied with many blood and lymph vessels, the 



