578 VETERINARY PHYSIOLOGY 



consumption of oxygen by the kidney is increased, indicating 

 an increased metabolism (fig. 227). The renal cells are in fact 

 doing work. 



These last experiments seem to indicate that the cells of the 

 convoluted tubules are capable of secreting water as well as 

 solids. 



Large doses of caffeine poison the cells, and in this condition 

 a flow of urine without increased consumption of oxygen is 

 produced. This supports the view that filtration from the 

 glomeruli plays a part. 



The stimulating action of such drugs as caffeine is taken 

 advantage of in cases of heart-disease when the secretion of 

 urine is almost arrested from low arterial pressure and when 

 dropsy is rapidly advancing. The kidneys may be stimulated 

 to get rid of water by means of such diuretics until compensa- 

 tion of the heart is established. 



5. The fact that after drinking copious amounts of water a 

 urine of a lower osmotic pressure than the plasma may be 

 produced, can be equally well explained by an increased 

 secretion of water by the tubules as by the reabsorption of 

 solids by them. 



6. The action of extracts of the hypophysis cerebri in increas- 

 ing the flow of urine while actually lowering the arterial 

 pressure (p. 594) seems to indicate a direct stimulation of the 

 cells of the tubules. 



7. When a mixture of NaCl and of Na^SO^ are injected, the 

 proportion of the latter in the urine increases after some time, 

 and the conclusion has been drawn that the NaCl is being 

 reabsorbed to be returned to the blood. If this were the case 

 the cells would do work and the 0^ consumption should be 

 increased. But the injection of NaCl leads to a diuresis, as 

 explained above, which is not accompanied by increased 

 consumption of Oo, while, on the other hand, the diuresis 

 caused by Na„SO^ is accompanied by an increased metabolism 

 of the kidney "(fig. 227). 



An increased secretion of NaoSO^ seems to explain the facts 

 of the case just as well as a supposed increased absorption of 

 NaCl. Similarly, the fact that when NaCl is withheld, it 

 practically disappears from the urine, although it persists in the 

 blood may just as well be explained on the theory of a 



