10 R. G. HOSKINS 



i 

 Conditions Determining Internal Secretions 



In a classical treatise with which all students of endocrin science 

 should be familiar, Gley (1917) has considered at length the conditions 

 that determine whether or no any given organ can logically be included 

 in the endocrin congeries. 



Three conditions, while they suffice, must all be met before any given 

 structure can be placed definitely among the organs of internal secretion. 

 The determining conditions are, respectively, histological, chemical and 

 physiological. The cells of the organ or tissue in question must show 

 evidence of secretory function, such as the presence of granular pre- 

 cursors or mitochondria and the cells must exhibit a polarity in relation 

 to the excretory channels, the efferent vessels. Second, it is necessary 

 to demonstrate the presence of a peculiar chemical entity both in the 

 cells and the efferent blood or lymph. Finally, the blood or lymph must 

 be shown to exhibit pharmacodynamic or growth influencing properties 

 not demonstrable, or demonstrable only to much less extent in the blood 

 or lymph of the body in general. 



As a matter of fact, these conditions have not all been met in various 

 organs conventionally included among the endocrin glands. In case of 

 even the thyroid many attempts to meet the third criterion have been 

 unsuccessful. Of recent years, however, researches in Asher's and Can- 

 non's laboratories have perhaps satisfied the requirement by showing 

 that the reactions to epinephrin are distinctly modified by stimulation 

 of the nerves to the thyroid gland. In any case, however, the effects 

 of thyroid extirpation are so clean cut and characteristic, and the effects 

 of thyroid extract in alleviating the symptoms of thyroid deficiency are 

 so well marked that no reasonable doubt can be entertained that this 

 gland has an endocrin function. 



Histological Condition. The endocrin organs proper are without 

 ducts leading to the exterior and this is also true of the endocrin tissues 

 that are incorporated in the pancreas and the gonads. These structures 

 aro permeated by a rich supply of blood vessels with which their cellular 

 elements aro in intimate connection, toward which they are polarized, and 

 into which their secretions are discharged. Eegarding such a structure 

 as the pancreas or the liver, organs which are provided with ducts for 

 external discharge of their secretions but which also discharge directly 

 into the blood stream, a double polarity is manifested. Similarly in the 

 duodenojejunal mucous membrane this dual polarity is seen. The cells 

 discharge their digestive secretions into the intestinal cavity, but they 

 also deliver to the blood a substance, secretin, which serves as a hormone 



the pancreas. The processes of digestion and absorption in the ali- 

 mentary tract afford various other examples of cell layers which discharge 



