90 LECTURE V. 



secreting the digestive ferment, is spoken of as that of an internal secretion. 

 An internal secretion is something formed within a glandular organ and 

 given off to the blood or lymph. The ordinary pancreatic juice is called 

 an external secretion. 



The discovery by Langerhans 1 of a peculiar segregation of cells in the 

 pancreatic gland led to discussion as to whether the gland possesses partic- 

 ular cells for its various functions. These cell-forms called islands of Lan- 

 gerhans which stand out very sharply from the other cells in the gland 

 differ from the latter not only in outward appearance, but, by the fact that, 

 unlike the ordinary secretory cells, they have no connection with the exit 

 ducts from the gland. More recently Diamare and Kuliabko 2 have taken 

 up anew the question as to the significance of these cells. They studied 

 the pancreatic glands of the Teleostei because in these animals the islands of 

 Langerhans are relatively large, and preparations of them may be easily 

 made free from the other cells of the pancreas tissue. They found that 

 only the ordinary cells of the gland produced an amylolytic ferment, 

 while the cells of the islands of Langerhans possessed the power of destroy- 

 ing dextrose. This sums up all that we know concerning these islands of 

 Langerhans, and it remains undecided as to whether they form an internal 

 secretion or not. We shall come back to this point in the discussion of 

 diabetes. 



Changes in the pancreatic gland had been observed before the discovery 

 of pancreatic glucosuria, namely in the so-called diabetes mellitus of 

 man. Although, in discussing the phenomena of this pathological degen- 

 eration, we are leaving the proper field of physiological chemistry, we will, 

 nevertheless, take it up more or less in detail, because in this disease we 

 have in a certain sense an experiment brought about by Nature, which 

 serves to give us some insight into the normal metabolism of carbohy- 

 drates. We shall, however, discuss the disease only in so far as it is directly 

 or indirectly connected with the metabolism of carbohydrates, and leave 

 the discussion of the remaining clinical symptoms of this very interesting 

 disease to the text-books on clinical medicine. 



Diabetes has been known for a long time. 3 The Indian and Arabian 

 physician of the Middle Ages recognized the fact that associated with the 

 disease was the elimination of a sweet substance in the urine. It remained 

 for Thenard, in 1806, to isolate this sweet substance; Chevreul crystallized 



1 Beitrage zur mikroskopischen Anatomie der Bauchspeicheldriisen, Berlin. 

 Dissert. 1869. 



2 Zentr. Physiol. 18, 432 (1904). 



3 Cf. Max Salomon: Geschichte der Glukosurie von Hippokrates bis zum Anfang des 

 19 Jahrhunderts, Deutsches Arch. klin. Med. 8, 489 (1871), and E. O. v. Lippmann: 

 Zur Geschichte des diabetischen Zucker. Chem.-Ztg. 29, 1197 (1905). 



