406 A MANUAL OF PHYSIOLOGY 



would not have destroyed its power to excrete water if it 

 possessed this power in any great degree ; and the glomeruli 

 and their capsules are the only other part of the renal 

 mechanism which can have been affected. The fact that 

 in birds and serpents, whose urine is solid or semi-solid, the 

 glomeruli are smaller than in mammals is corroborative 

 evidence that the glomeruli have to do with the excretion of 

 water. 



An attempt has recently been made by Sobieranski, on the strength 

 of a reinvestigation of the microscopical appearances presented by 

 the kidney after injection of pigments into the blood, to revive 

 Ludwig's theory that absorption takes place from the tubules. He 

 asserts that, although pigment granules are found in the rodded 

 epithelium, they are always near the lumen of the tubule, never near 

 the basement membrane. From this he concludes that the pigment 

 is not passed through the cells from the blood, but absorbed by them 

 from the tubules after excretion by the glomeruli. It cannot, how- 

 ever, be admitted that his observations are decisive. 



Nussbaum's experiments were founded on the anatomical 

 fact that the kidney of batrachians, and, indeed, that of fishes 

 and ophidia as well, has a double blood-supply. The renal 

 artery gives off afferent vessels to the glomeruli, and the 

 vena advehens or renal portal vein breaks up, like the 

 portal vein in the liver, into a plexus of capillaries sur- 

 rounding the tubules, with which plexus the efferent arterioles 

 of the glomeruli communicate. By tying the renal arteries 

 in the frog, Nussbaum thought he could at will stop the 

 circulation in the glomeruli, and he found that after this was 

 done, sugar, peptones and egg-albumin, injected into the 

 blood, no longer passed into the urine, although they readily, 

 did so when the arteries were not tied. Urea, however, was 

 still eliminated by the kidneys after ligature of the renal 

 arteries, and water along with it. He concluded that the 

 Malpighian corpuscles have the power of excreting water, 

 jugar, peptone, and albumin, while the epithelium of the 

 tubules excretes urea as well as water. 



Adami has since shown that the circulation in the glomeruli 

 is not wholly stopped by Nussbaum's operation, for there is 

 a certain amount of anastomosis between the arteries of the 

 generative organs and the renal arteries. He therefore 



