HISTORICAL DEVELOPMENT AND DEFINITION 5 



of the body in contradistinction to the assumption of a nervous correlation, 

 which formerly was almost all-sufficient. This distinction is indeed not to be 

 maintained so rigidly for, as we shall see later on, it must be assumed that 

 to many specific ductless glandular secretions must be ascribed an important 

 and, after its fashion, a quite definite influence on the condition of excita- 

 tion of the nervous system. We cannot indeed exclude the question as to 

 whether the action of the ductless glandular secretions does not come about 

 through alterations in the metabolic processes in the various parts of the 

 somatic and vegetative neurones (ganglion-cells, myoneural junctions, etc.). 

 A. Biedl happily expresses these changes in our views by the dictum: "For- 

 merly every correlation of organs was regarded as nervous; to-day, however, 

 even nervous actions are regarded as brought about chemically." Bayliss 

 and Starling have found that under the influence of the acid gastric juice 

 upon the epithelial cells of the intestinal mucosa a substance is secreted by 

 the latter that brings about through the circulation the secretion of pan- 

 creatic juice. They call such chemical messengers hormones (from 6^/iaw = 

 I call), a designation that now has found almost general use also as applied 

 to the specific secretions of the ductless glands. With such a general 

 application of the meaning of the internal secretions, not much is to be 

 gained for clinical purposes, as may readily be seen. Nor is a morphological 

 definition of the ductless glands possible, as Biedl has pointed out. The histo- 

 logical structure of the individual ductless glands varies according to their 

 genesis from the different germinal layers. Whether the specific secretions 

 of the ductless glands are to be separated from the other hormones through 

 their chemical characteristics cannot be answered at all at the present day. 

 Anatomy, morphology, embryology, experimental physiology, and patholog- 

 ical chemistry do not furnish to-day a satisfactory characterization of the 

 ductless glandular system. Up to the present, the demonstration that an 

 individual ductless gland belongs to a system is furnished most distinctly 

 by clinical observation, particularly by the intimate reciprocal relations of 

 the ductless glands under physiological and pathological conditions. 



It appears to me, therefore, that first and foremost it is more important for 

 the clinical point of view not to associate the meaning of internal secretion 

 exclusively with the ductless glands. I might formulate this standpoint in 

 the following way: probably very many cell-complexes of the animal organ- 

 ism possess an internal secretion. We may designate the totality of all cell- 

 complexes provided with an internal secretion a hormonopoietic system. There 

 are, however, a series of organs the proper function of which we must regard as the 

 production of especially important hormones, which are provided with powerful 

 physiological characteristics. It is a common property of these organs that they 

 separate out their specific secretion directly into the blood-path. We therefore 

 call them ductless glands, and their collective total the ductless glandular system. 



The recognition that the ductless glands form a system was of great sig- 



