206 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



is eliminated from the body by the kidneys, but it is known not to be formed 

 in these organs. Modern investigations (see p. 000) have seemed to show con- 

 clusively that this substance is formed mainly within the liver from some 

 antecedent substance (carbamate of ammonia) which arises in the proteid tissues 

 generally, but is not prepared for final elimination until in the liver or else- 

 where it is converted into urea. Here again the liver-cells perform a metab- 

 olism for the good of the organism as a whole, and the act of passing out 

 the urea into the blood may be regarded as an internal secretion. It is quite 

 possible that in still other ways the liver-cells add to the blood elements of 

 importance to the tissues of the body as, for example, in the conservation and 

 distribution of the iron of broken-down haemoglobin (see p. 275), or in the syn- 

 thetic combination of the products of putrefaction formed in the intestines (indol, 

 skatol, phenol, etc.) with sulphuric acid (see p. 263) ; but concerning these mat- 

 ters our knowledge is not yet sufficiently definite to make positive statements. 

 Pancreas. The importance of the external secretion, the pancreatic juice, 

 of the pancreas has long been recognized, but it was not until 1889 that Yon 

 Mehring 1 and Miukowski proved that it furnishes also an equally important 

 internal secretion. These observers succeeded in extirpating the entire pan- 

 creas without causing the immediate death of the animal, and found that in 

 all cases this operation was followed by the appearance of sugar in the urine 

 in considerable quantities. Further observations of their own and other experi- 

 menters have corroborated this result and added a number of interesting facts 

 to our knowledge of this side of the activity of the pancreas. It has been 

 shown that when the pancreas is completely removed a condition of glycosuria 

 inevitably follows, even if carbohydrate food is excluded from the diet. More- 

 over, as in the similar pathological condition of glycosuria or diabetes mellitus 

 in man there is an increase in the quantity of urine (polyuria), and of urea, 

 and an abnormal thirst and hunger. These symptoms in cases of complete 

 extirpation of the pancreas are followed by emaciation and muscular weak- 

 ness, which finally end in death in about two weeks or less. If the pancreas 

 is incompletely removed the glycosuria may be serious, or slight and transient, 

 or absent altogether, depending upon the amount of pancreatic tissue left. 

 According to the experiments of Von Mehring and Minkowski on dogs, a 

 residue of one-fourth to one-fifth of the gland may be sufficient to prevent the 

 appearance of sugar in the urine. The portion of pancreas left in the body 

 may suffice to prevent glycosuria, partly or completely, even though its con- 

 nection with the duodenum is entirely interrupted, thus indicating that the 

 suppression of the pancreatic juice is not responsible for the glycosuria. The 

 same fact is shown more conclusively by the following experiments : Glycos- 

 uria after complete removal of the pancreas from its normal connections may 

 be prevented by grafting a portion of the pancreas elsewhere in the abdominal 

 cavity or even under the skin. The ducts of the gland may be completely 

 occluded by ligature or by injection of paraffin without seriously disturbing 



l Archiv fur exper. Pathologic und Pharmakologie, 1890, Ed. xxvi. S. 371. See also Minkow- 

 ski, Ibid., 1893, Bd. xxxi. S. 85, for a more complete account. 



