102 PHYSIOLOGY CHAP. 



result. On the other hand, the conclusions of Hedon. Gley, Lepine, 

 and many others were negative. To us it seems too large an order 

 to assert that artificial injections of glandular pulp can replace a 

 physiological function which develops in a continuous and regular 

 manner, or to give a decisive value to negative results in such 

 questions. 



A very ingenious experiment, which tells in favour of a true 

 internal secretion of the pancreas, is that of Forschbach (1908) with 

 the method of parabiosis. This consists in uniting two animals of 

 the same species and litter with a triple suture (cutaneous, 

 muscular, peritoneal). In the animals thus operated on, there is 

 an exchange of blood by the blood-vessels and lymphatics of the 

 two communicating abdominal cavities, and it has been shown 

 that many substances (iodine, sugars, alkali, etc.) injected into 

 one animal pass rapidly into the other. 



On extirpating the pancreas from one of the two dogs in 

 parabiosis, pathological disturbances do not set in with the severity 

 described above : in some cases they are very slight, but become 

 aggravated as soon as the depancreatised dog is separated from 

 the other. 



Biedl observed permanent glycosuria after ligation of the 

 thoracic duct, or when the whole of the lymph had been drawn off 

 externally, and found (with Offer, 1907) that this experimental 

 diabetes disappeared on injecting lymph, which suggests that the 

 internal secretion of the pancreas may be discharged by the 

 lymphatic system. 



These observations render the hypothesis of an internal 

 secretion the most probable among the many that have been 

 proposed to explain the internal function of the pancreas. 



X. Given the existence of an internal function of the pancreas, 

 and assuming it to be served by a special secretion, Laguesse, 

 Schafer, Opie, and others formulated a theory that has been widely 

 accepted. The two secretions of the pancreas, external and 

 internal, are held to be distinct functions of different cells, the 

 former being served exclusively by the alveoli, the second by the 

 islets of Langerhans. 



The morphological arguments for this theory are, however, 

 inadequate, and too much a matter of controversy to be conclusive. 

 They rest on the well-known fact that the islets are provided 

 with numerous blood-vessels, and on the assertion (supported by 

 very few authors) that they are completely invested by a capsule of 

 connective tissue and contract no relations with the excretory 

 ducts. 



If this could be proved, the insular theory would obviously 

 have a valid anatomical basis. Even so, however, the possibility 

 that the alveoli also contribute to the internal secretion would not 

 be excluded. Moreover, the fact that the islets contain numerous 



