THE SYMPATHETIC SYSTEM 353 



If this gland is slightly affected it is stimulated; if, how- 

 ever, it is very much degenerated, the extract of liver 

 remains inactive, just as digitalis becomes inactive when 

 the myocardium becomes affected. By this mechanism 

 we can explain the action of most of the glandular extract. 

 "An extract of an organ, given in proper doses," says 

 Hallion, "stimulates electively, in the subject receiving it, 

 the functions of the organ of the same name." 



This law appears to be general. It is thus, as the last- 

 named authority has shown, that this same law applies to 

 the extract of thyroid, the most perfect type of internal 

 secretion having a substitute action. "It has been shown 

 that outside of its function as a substitute to the deficient 

 thyroid, it also acts on the remaining thyroid as a 

 stimulant which can be explained in the following manner: 

 Thyroid extract contains a variety of specific substances. 

 These are, independent of the colloidal material, the 

 substances which only the thyroid can manufacture and 

 which it utilizes to build up its own protoplasm or manu- 

 facture its secretions. When these substances are intro- 

 duced into the circulation, it seems as if the thyroid recog- 

 nizes them ; it takes hold of and utilizes them since they 

 are received already made up either to repair its own 

 structures or to help it to functionate." 



One of the most definite demonstrations of this was 

 shown by Ballet and Enriquez. They caused the appear- 

 ance of Basedow's syndrome by the injection of thyroid 

 extracts and obtained a hypertrophy of the body of the 

 thyroid which, microscopically, showed stimulation and 

 hyperplasia. Renon and Arthur Delille, by using smaller 

 doses in rabbits, were able to show on histological exam- 

 ination of the gland a marked increase of colloidal material 

 secreted in the vesicles. 



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