DUCTLESS GLANDS 93 



known nature of its functions insures it from bothersome investigation 

 at the hands of medical men {"Die unbeJcannte Funhtion der Nehen- 

 niere sichert dieses Organ von Idstigen Nachfragen in der Heilwissen- 

 scliaft"). 



If we regard the lungs or the individual cells of the body tissues pro- 

 visionally as ductless glands, then it will be perceived that the truth of 

 the equation formulated by Legallois had already been demonstrated 

 quantitatively when Lavoisier proved that inspired air is converted into 

 carbon dioiide and water, and when Lagrange, through his pupil 

 Hassenfratz, proved that the oxygen in inspired air, being dissolved in 

 the blood, takes up carbon and hydrogen from the body tissues as the 

 blood courses through them (1791). We now know that the respira- 

 tory center in the medulla is stimulated by the CO2 in the venous blood, 

 which Lavoisier and Lagrange had shown to be, in effect, a true meta- 

 bolite, or waste-product of tissue-oxidation. Their work was in fact the 

 starting point of the chemical study of metabolism, which received its 

 next great advancement in Claude Bernard's study of glycogen; for 

 although the latter may not be, in the strict sense, a true internal secre- 

 tion, discharged from a gland into the blood, yet its investigation led 

 Bernard to the classical statement of the doctrine of internal secretions 

 as such: 



In animals, the glycogenic secretion is an internal secretion because it is 

 discharged directly into the blood. I have considered the liver, as found in the 

 higher vertebrates, as an organ with a double secretory function. It seems to re- 

 unite, in effect, two distinct secretory elements and it represents two secretions, 

 one externa], the biliary secretion, the other internal, the glycogenic secretion, 

 which is discharged into the blood.is 



In the year 1843, Claude Bernard, in his graduating thesis, made 

 the discovery that cane sugar is acted upon by the gastric juice, being 

 converted by it into dextrose. This experimental fact led to a train of 

 reasoning which was to revolutionize the physiology of nutrition and 

 metabolism and at the same time to introduce the new concept of inter- 

 nal secretions and to be the starting point of the experimental produc- 

 tion of disease by the artificial use of chemical and physical agencies. 

 All carbohydrates, Bernard reasoned, must get into the blood in the 

 form of dextrose. "What becomes of this dextrose?" he next inquired. 

 Somewhere between the alimentary canal {via the portal vein) and the 

 liver, between the liver {via the right heart) and the lungs, between the 

 lungs {via the left heart) and the various body tissues, this dextrose is 

 either destroyed and disappears or is transformed into some other sub- 

 stance. If the locus of this transformation could be discovered and its 

 activities inhibited, an artificial diabetes might be produced by the 

 induction of excess of sugar in the blood. On feeding a dog on rich 

 sugar diet and killing it at the height of digestion, he found the hepatic 

 veins loaded with dextrose, and although this looked at first as if the 



18 Bernard, "Lemons de physiologic experimentale, " Paris, 1855, I., 96. 



