912 PHYSIOLOGY 



into the blood stream arid is carried to all the tissues of the body to 

 act as a necessary link or arnboceptor in the assimilation of carbo- 

 hydrates. Until recently there was no positive evidence for this view. 

 Administration of the pancreas itself or of extracts of the pancreas, 

 either by the mouth or subcutaneously, has no definite effect on the 

 course of the disorder. On the other hand, an isolated heart from a 

 diabetic animal, when perfused with blood plus glucose from the same 

 animal, is unable to consume glucose ; but, on adding a decoction of 

 fresh pancreas, a consumption of sugar is observed, which may attain 

 the same degree as that in a normal heart (Knowlton and Starling). 

 If the pancreatic cells do produce such a hormone, the production 

 must be a gradual one, in response to the needs of the body, and is 

 not attended by the accumulation of sufficient quantities of the 

 hormone in the gland as to exert a curative influence on the whole 

 animal when administered in extracts of the gland. It has been 

 suggested that the islets of Langerhans are responsible for this 

 hypothetical internal secretion, and changes in these islets have 

 been described in cases of diabetes in man. There is no satisfactory 

 evidence for this assumption, and, as we have seen already, it seems 

 possible that the islets represent a stage in the development of the 

 ordinary secreting tissue of the gland. 



(5) DIABETES IN MAN. In its severer forms the diabetes of man 

 resembles very closely that produced in the dog by total extirpation 

 of the pancreas. The output of urine is largely increased and the 

 frequency of micturition is often the first symptom noticed. On 

 examination the urine, though light in colour, is of a high specific 

 gravity, 1030 to 1035, and may contain from 5 to 10 per cent, of sugar. 

 The appetite is largely increased, but in spite of the large amount of 

 food taken the body wastes. The excessive quantity of fluid lost by 

 the body gives rise to a constant thirst. The patient may die after 

 some months or years in a condition of diabetic coma. Warning of 

 the onset of this condition is given by the rise of ammonia in the urine 

 and by the appearance of oxy butyric and diacetic acids. The 

 breath may smell of acetone, and this substance may also be present 

 in the urine. On the other hand, the diabetic state is attended by 

 diminished resistance of the tissues to infection. A pimple may 

 become a carbuncle ; a slight sore on the foot may give rise to a 

 rapidly spreading gangrene of the lower extremity ; tubercular infec- 

 tion of the lungs spreads rapidly to the whole organ so as to simulate 

 pneumonia. The patient may thus die of some such intercurrent 

 infection before the onset of coma. In a few cases the pancreas 

 is found to be atrophied or diseased, but in the large majority no 

 marked pathological change is to be observed in this organ. Yet the 

 condition is essentially similar to that which occurs in pancreatic 



