INTRODUCTION 23 



entiate again, re-forming structural substances similar to those formerly 

 possessed, and perhaps function normally. But when de-differentiation 

 has proceeded far enough, under abnormal conditions, a metaplastic trans- 

 formation may result, the cells developing characteristics which they did 

 not formerly have. 



Some at least of the senile alterations suggest the operation of endocrin 

 factors. The scantiness and dryness of the hair, the dryness of the skin, 

 the manifestations of depressed metabolism in the osseous structures, and 

 the tendency to chilliness are such changes as might result from deficient 

 thyroid secretion. Indeed, it has been claimed that these alterations 

 can to a considerable extent be obviated or ameliorated by the circumspect 

 administration of thyroid gland substance. As a matter of fact, the 

 thyroid gland in old age shows anatomical alterations such as atrophy and 

 sclerosis, which might well result in functional deficiencies, but whether 

 these changes antedate the senile manifestations just mentioned apparently 

 has not been determined. In old dogs Goodpasture found the thyroid 

 glands smaller than normal. He noted also a marked irregularity in 

 the distribution of the colloid and occasional areas of metaplasia. In 

 three instances multiple cysts were found ; these were lined with three or 

 four layers of epithelium and the layer nearest the lumen was partially 

 or completely differentiated. 



Little is known regarding changes in the parathyroid glands in old 

 age. The tremors of paralysis agitans, which is not an infrequent disease 

 of old age, have been ascribed to parathyroid deficiency and there are in 

 the literature reports of successful treatment of the condition by para- 

 thyroid opotherapy. The evidence at present available does not permit 

 any very definite conclusions, however, as to the importance of the 

 parathyroid factor. Goodpasture noted little deviation from the normal 

 in case of senile dogs. 



The pigmentary alterations of the skin are somewhat suggestive of 

 those known to result from adrenal deficiency. In view of the fact, 

 however, that pigmentation of the skin can result from a variety of 

 causes, such evidence is by no means convincing. In his senile dogs 

 Goodpasture, as a matter of fact, found that the suprarenals were usually 

 larger than normal and their surface was irregular with smooth and 

 more or less spherical protuberances 1 to 20 mm. in diameter, usually 

 multiple and occurring in both glands. There was commonly great irreg- 

 ularity in the architecture of the cortex due to a combination of atrophy 

 in some parts and hyperplasia in others. There were no outspoken de- 

 generative changes constantly demonstrable in the cells, but there were 

 indications of a gradual disappearance and replacement of the paren- 

 chyma. Indirect evidence of degeneration was found in the presence in 

 the lymph spaces of a considerable number of phagocytes filled with 

 brownish, finely granular pigment. Hyperplastic changes were found in 



