SECRETION OF THE DUCTLESS GLANDS. 797 



in man following upon a greatly dilated stomach histological ex- 

 amination of the parathyroids snowed evidences of active cell mul- 

 tiplication. The inference in this case would seem to be that the 

 toxins resulting from the gastric conditions had aroused a com- 

 pensatory increase in parathyroid activity. No precise statement, 

 however, can be made regarding the physiology of the parathy- 

 roids. The old view that they represent follicles of undeveloped 

 or embryonic thyroid tissu'e is not supported by experiments. We 

 must believe rather that the parathyroids and the thyroids are 

 different structures ; their histology is different, they have different 

 embryological origins, and physiologically they subserve different 

 functions. Chemically also there is perhaps a distinction in that 

 the iodin compounds so characteristic of the thyroid tissue are said 

 by some observers to be absent from the parathyroids. Some 

 observers contend that there is a correlation of functions between 

 the thyroids and parathyroids, but the proofs for this view are not 

 convincing. 



The General Nature of the Functions of the Thyroids and 

 Parathyroids. Disregarding the difference in function between 

 these two bodies, it is quite evident from the facts given that they 

 exercise an important control over the processes of nutrition of the 

 body, and especially perhaps over those of the central nervous 

 system. How is this control exerted? Two general points of view 

 have been advocated. According to one theory, the thyroid tis- 

 sues elaborate a special internal secretion, characterized by its 

 contents in iodin. This secretion is given off to the lymph or blood, 

 is carried to the tissues, and there exercises a regulating action of 

 an important or indeed essential character. Excision or atrophy 

 of these bodies results in a loss of this secretion and a consequent 

 malnutrition or perverted metabolism in other tissues of the organ- 

 ism. This view prevails for the case of the thyroids. According 

 to another point of view the function of these bodies is to neu- 

 tralize or destroy toxic substances formed in the metabolism of 

 the rest of the body, as the liver, for instance, destroys the toxic 

 character of the ammonia compounds by converting them to urea. 

 On this theory the removal of the thyroid tissues results in the 

 accumulation of toxic substances in the blood and the animal dies 

 by a process of auto-intoxication. As stated above there is some 

 evidence for this view in the case of the parathyroids. 



Cyon's View of the Function of the Thyroid. Cyon in numerous 

 publications has advocated a different view of the function of the thyroids. 

 These bodies have a very large vascular supply, and this author assumes that 

 this area serves as a vascular shunt or flood-gate to protect mechanically 

 the circulation in the brain. The dilatation of the thyroid area under con- 



