SECRETION. 411 



by an experiment as follows: The liver of an animal recently living 

 is removed from the body and its vessels perfused continuously with 

 blood (the urea content of which is known) containing the ammonium 

 salts. An analysis of this blood shows, after a time, a diminution 

 of these salts, and a large increase in the amount of the urea. The 

 leucin and tyrosin which result from the prolonged action of pan- 

 creatic juice on hemi-peptone are also capable of being converted to 

 urea by the hepatic cells, and in all probability are so disposed of. 

 Destructive diseases of the liver e. g., acute yellow atrophy, sup- 

 puration, cirrhosis largely diminish the production of urea, but in- 

 crease the quantities of the ammonium salts in the urine. The same 

 is true when the liver cells are destroyed during acute phosphorus- 

 poisoning. 



VASCULAR OR DUCTLESS GLANDS. 

 INTERNAL SECRETIONS. 



The metabolism of the body generally, as well as that of individual 

 organs, has been shown to be related not only to the physiologic ac- 

 tivity of such organs as the liver and pancreas, but also to the activity 

 of the so-called vascular or ductless glands. The influence of the 

 pancreas in regulating the production of glycogen by the liver, and 

 the influence of the liver in the maintenance of the general metabo- 

 lism through the production of glycogen and the formation of urea, 

 are now established facts. That the vascular or ductless glands to 

 an equal extent, though perhaps in a different way, assist in the main- 

 tenance of physiologic processes, appears certain from the results 

 of animal experimentation. The explanation given for the influence 

 of these glands is that they produce specific substances, which are 

 poured into the blood or lymph and carried direct to the tissues, to 

 the activities of which they appear to be essential; for without these 

 substances the nutrition of the tissues declines and in a short time 

 a fatal termination ensues. 



Inasmuch as these partly unknown substances are formed by cell 

 activity and are poured into the interstices of x the tissues, they have 

 been termed "internal secretions." Though the term internal secre- 

 tions is applicable to all substances which arise in consequence of 

 tissue metabolism, and which, after being poured into the blood, 

 influence in varying degrees and ways physiologic processes, yet the 

 term in this connection will be applied only to the secretions of the 

 thyroid gland, hypophysis cerebri, and adrenal bodies. 



Thyroid Gland. The thyroid gland or body consists of two lobes 

 situated on the lateral aspect of the upper part of the trachea. Each 

 lobe is pyriform in shape, the base being directed downward and on a 

 level with the fifth or sixth tracheal ring. The lobe is about 50 mm. 

 in length, 20 mm. in breadth, and 25 mm. in thickness. As a rule, 



