Abstract
There is no doubt that in the development of normal tissues structural differentiation and functional differentiation parallel each other, but in the case of tumors little is known as to whether any such parallelism exists. One obvious reason for this is that very few of the tissues from which tumors most frequently develop have any readily estimated physiological attributes. Beginnings have been made in this direction in the case of adrenal tumors (hypernephromas) through investigations for the presence of the specific pressor substance.1 So also considerable work has been done with lipomas by way of chemical analysis and comparison with the fat of normal adipose tissues.2 For investigations in this field it has long seemed to us that the thyroid offered most favorable conditions. Thus its architecture is simple; it is localized, easily accessible and has a wide range of morphological variations within the

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