KIDNEYS. 427 



covering the glomeruli would offer great resistance to filtration ; 

 that if the renal vein is ligated and the pressure within the 

 glomeruli thereby increased, not only is the flow of urine not in- 

 creased, but it is actually abolished; and, finally, that filtration 

 will not explain the increased flow of urine when water and crys- 

 talloid substances are increased in the blood. Heidenhain, as 

 already stated, believes that the cells of the glomerular epithelium 

 act as secretory cells do elsewhere, and by the power which they 

 possess as living cells eliminate water and inorganic salts, espe- 

 cially sodium chlorid, from the blood. 



In commenting on these opinions, Starling, to whose admirable 

 article on " The Mechanism of the Secretion of the Urine/ 7 in 

 Schafer's Text-book of Physiology, we are much indebted, says : 

 " It seems probable that in the glomeruli the process is largely 

 if not exclusively physical," and that " we have at present no evi- 

 dence that the cellular covering of the glomeruli acts otherwise than 

 passively in the production of the glomerular part of the secre- 

 tion." He also refers to the researches of Munk and Senator, who 

 have reached the conclusion that water and part of the urinary salts, 

 especially sodium chlorid, are transuded through the glomeruli iii 

 direct consequence of the blood-pressure i. e., by a process of fil- 

 tration, although the rapidity of the blood-flow is equally important. 

 It is also generally accepted that when serum-albumin, hemo- 

 globin, or dextrose escapes from the blood and becomes a constitu- 

 ent part of the urine, this takes place while the blood is passing 

 through the glomeruli. 



The oncometer (p. 338) has been largely used in connection 

 with the various experiments which have been conducted to deter- 

 mine the effects of increased and diminished blood-pressure on the 

 excretion of urine by the kidney. 



Excretion of Urea, Uric Acid, etc. Bowman, in his views as 

 to the manner of the formation of urine, expressed the opinion 

 that the tubes and their plexus of capillaries were probably the 

 parts concerned in the secretion of the substances forming this 

 second group of urinary constituents, and this is the generally 

 accepted view of the authorities of the present day. It is also 

 probably true that some water, sodium chlorid, sulphates, and 

 phosphates are eliminated from the blood in this part of its course 

 through the kidney. The efficient agents in this elimination are 

 the cells lining the tubules, and especially those in the convoluted 

 portions. 



Effects of Removal of the Kidneys. Removal of a single kidney 

 for a diseased condition of that organ, constituting nephrectomy, 

 is not an uncommon operation at the present day. After the 

 operation the remaining kidney enlarges and performs the func- 

 tions of both. Removal of both kidneys is followed by a fatal 

 result. 



