626 INTERNAL SECRETION 



haus). Some authors, indeed, have gone so far as to say that in all 

 cases of diabetes mellitus there is disease of the pancreas, but of this 

 there is no evidence. 



Ligation, or the establishment of a fistula, of the thoracic duct, 

 causes glycosuria in dogs. It is possible that this is really a mild 

 form of pancreatic diabetes, due to interference with the supply of 

 the internal secretion of the pancreas, or of that part of it which 

 reaches the blood by the lymph- stream (Tuckett). 



Pfliiger has brought forward evidence that it is not the removal of the 

 pancreas, as such, but the section of certain nerves running into or 

 through it from the duodenum, which is the cause of the glycosuria. 

 For when these nerves are divided or the duodenum removed while the 

 pancreas remains untouched, the result is the same as if the pancreas 

 itself had been excised. He imagines that these nerves are ' anti- 

 diabetic ' that is, in some way oppose the production of sugar while 

 nerves coming from the so-called ' sugar centre ' in the bulb (the centre 

 assumed to be affected in the puncture experiment) favour sugar pro- 

 duction. Between these the normal balance is struck in health; it is 

 the upsetting of this balance by the crippling of the duodenal fibres 

 which is at the bottom of ' pancreatic ' diabetes. It is too early to 

 appraise the value of this conception, especially as the facts upon which 

 it is founded have only been clearly established for frogs, and it is 

 doubtful whether they can be extended to mammals . But if these nerves 

 end in the pancreas, and do not simply run through it, say, to the 

 liver, it is possible that they act on the sugar metabolism by regulating 

 the internal secretion of the pancreas. 



iSexual OrgansX-^The influence of castration in preventing the 

 development of trie sexual characters, and especially the physical 

 and psychical changes that normally occur at puberty, is also due 

 to the loss of the internal secretion of the generative glands, and 

 does not appear to depend at all upon the loss of nervous impulses 

 arising in these organs. )In Herdwick sheep an outstanding sexual 

 difference is the presence of horns in the males, their absence in 

 the females. Removal of the testes from ram lambs arrests further 

 growth of horns forthwith and at any stage of development. The 

 retention of the epididymes, provided that the testes proper are 

 removed, does not alter the result of castration in the least. The 

 removal of one testicle slows horn growth without arresting it 

 (Marshall and Hammond). In partially castrated cocks it has been 

 seen that, so long as a portion of one testicle remains, the male 

 characters are preserved, but after removal of this residue the 

 comb and wattles wither in a few weeks (Hanau). At the breeding- 

 time the muscles of the forearm of the brown land frog (Rana 

 fusca) become hypertrophied in the male, so that it can more tightly 

 hold the female. At the same time the balls of the toes increase 

 in size, and become covered with a peculiar black growth. After 

 the breeding season these secondary sexual characters disappear. 

 If the male frog is castrated, the periodic return of these phenomena 

 does not occur, but the presence of one testicle suffices for their 



