448 THE HUMAN BODY 



but many cases show on autopsy very well marked lesions of the 

 Islands of Langerhans. We may thus conclude with fair cer- 

 tainty that the disease is one affecting these Islands, and that its 

 symptoms are the result of more or less complete failure of the 

 hormone formed by them. 



Diabetes from Increased Permeability of the Kidney-Cells to 

 Sugar. The injection of a certain drug, phlorhizin, into the cir- 

 culation is followed by a glycosuria which is due to alterations in 

 the kidney. These are of such a sort that the kidney-cells, instead 

 of removing only sugar in excess of 0.2 per cent, take all that 

 comes to them. The result, of course, is a great waste of this 

 valuable fuel, requiring greatly increased consumption of carbo- 

 hydrates to make it good. This form of diabetes has been pro- 

 duced experimentally in animals, for purposes of study, but 

 occurs rarely, if at all, as a disease of man. 



The Absorption of Proteins. The nature of protein absorption 

 has been until recently one of the great unsolved problems of 

 physiology. Even at present we know much less about it than 

 about most other physiological problems of equal importance ; but 

 within recent years physiologists have succeeded in putting to- 

 gether the various facts that have been gathered on the subject, 

 and have based on them a very interesting theory of protein ab- 

 sorption, which seems very likely to be proved true. 



The great difficulty which has always confronted those who 

 have tried to analyze the process has been that no matter how 

 much protein was being absorbed from the alimentary tract, it 

 was never possible to demonstrate any perceptible increase in the 

 protein content of the blood in the portal vein or of the lymph in 

 the lacteals. In other words, as soon as the protein passed through 

 the walls of the alimentary canal it disappeared. When it became 

 known that proteins are split in digestion into amino acids there 

 were many attempts made to find these in the blood or lymph 

 draining away from the gut, but without success. We know, of 

 course, that the proteins must be absorbed somehow, and must be 

 taken up either by blood-capillaries or lacteals. The latter all 

 drain into the thoracic duct, and it is easy to open this in such 

 fashion as to secure every drop of lymph that comes from the 

 intestine. Most careful analyses of lymph thus secured have 

 failed to show any change in the protein content of lymph during 



