ii EXTERNAL DIGESTIVE SECRETIONS 103 



blood-vessels is no proof that they serve the internal secretion to 

 the exclusion of the alveoli. It is still conceivable that the 

 internal secretion of the pancreas may be discharged by the 

 lymph capillaries. Biedl's observations as previously quoted 

 support this hypothesis. 



Morbid anatomy does, indeed, support the view that the 

 islets are the exclusive organs for the internal secretion of the 

 pancreas. Numerous observations (Hanseinann, Opie, Gutemann, 

 Karakascheff, Ssobolew, Herxheimer, Schmidt, Sauerbeck, Visentini, 

 Herzog, Reitmann, etc.) show that the pancreas may exhibit 

 different features in human diabetes. In some cases there is no 

 alteration either of alveolar or of insular tissue. But in the great 

 majority of cases the pancreas is profoundly and diffusely altered, 

 both in the alveoli and in the islets. It is rare for the 

 degeneration to involve alveolar tissue only, still more rare that 

 the changes should be confined to the islets. 



The rare cases of diabetes with a healthy pancreas prove that 

 this disease is not necessarily pancreatic in origin ; which does not 

 alter the fact that the pancreas normally discharges an internal 

 secretion which affects carbohydrate metabolism. 



The rare cases of diabetes in which either the islets alone 

 or the alveoli alone are modified, cannot be taken as a decisive 

 argument in favour of the theory which ascribes the internal 

 secretion of the pancreas exclusively to the islets (Laguesse) or to 

 the alveoli (Hansemann); at most they suggest the hypothesis 

 that both these tissues co-operate actively in the normal internal 

 secretion of the pancreas. 



Experiments with the object of localising the external and 

 internal secretions of the pancreas in its two tissues have been 

 numerous. 



Schultze and Ssobolew (1900) were the first who maintained 

 the insular theory of internal secretion, starting from the fact that 

 after ligation of the ducts or internal pancreatic lobes in the 

 rabbit, the islets were left unaltered, while the alveoli were 

 modified and disappeared, without causing any true diabetes. 



The same fact had been described by Vassale ten years earlier, 

 but not with the intention of localising the internal secretion 

 in the islets : he merely sought to contradict Lewaschew, who 

 affirmed the unitary character of the two pancreatic tissues. 



Mankowski and Lombroso failed to confirm the results of 

 Schultze and Ssobolew. They found that ligation of the ducts in 

 the rabbit produced alterations not merely in the alveoli but 

 also in the islets, which diminished in size and number. 



Many other authors (Tiberti, Pende, Marassini, etc.) obtained 

 substantially the same results; some (Laguesse, Marassini), 

 however, argued from the greater resistance of islets as compared 

 with alveoli, that the absence of glycosuria must be referred to the 



