THE THYEOID GLAND AND ITS DISEASES 221 



kept at 30 to 37 C. for several days showed the following changes in 

 almost every case: The colloid content of the vesicles was increased in 

 amount, presented a uniform appearance, and stained rather intensely 

 with eosin; epithelial cells lining the vesicles were decreased in height, 

 often entirely flattened, their cytoplasm and nuclei appearing rather 

 compact and dense. That is to say, the thyroid had an inactive appear- 

 ance. On the other hand, in animals subjected to low out-of-doors winter 

 temperature, for the same period of time, the colloid material was dimin- 

 ished in amount and the epithelial cells hecame quite columnar, suggestive 

 of the appearances which we are accustomed to associate with hyper- 

 thyroidism. The same author has described variations in the gland after 

 the administration of morphin and quinin. 



Hygiene. According to Burget, unhygienic conditions alone are suf- 

 ficient to bring about hyperplasia, which is a partial confirmation of 

 McCarrison's observations. 



Inanition. Jackson (.&) has found that the thyroid responds very 

 quickly to inanition, and suggests that some of the structural changes fol- 

 lowing different diets may be due merely to their varying food values. 



Interpretation of Appearances. There are many confusing sources of 

 error in interpreting the histological appearances as we find them. In 

 the first place, the range of normal variation has not yet been established 

 for a single species. Regional variation must also be reckoned with, for 

 specimens taken from different parts of the same apparently normal gland 

 often present a very different appearance. It is for this reason that 

 serial sections are so useful in the study of small glands in experimental 

 series. Moreover, the thyroid gland undergoes autolytic changes with 

 extreme rapidity, so that the specimens should be taken as soon after 

 death as possible. Mechanical injury with the forceps and the drying 

 of a surface film of tissue before fixation must also be avoided. Cutting 

 with scissors is faulty technic, because of the pressure exerted on the 

 tissues. Specimens kept in salt solution at body temperature are ruined, 

 because autolysis is accelerated. The penetrating power of the fixative 

 must also be considered and due allowance must bo made. 



The problem of finding reliable histological criteria of secretory ac- 

 tivity is indeed a difficult one. Our older methods, rigorously controlled, 

 should be used hand in hand with the newer technic. Of the cytoplasmic 

 constituents recently discovered, the mitochondria alone have proved of 

 service in the investigation of human material. In experimental studies 

 the reticular apparatus and the secretion antecedents of Bensley deserve 

 more attention. 



