TENSION PHENOMENA OF LIVING ELK MI-NTS. 153 



exudate- is always greater than that of the blood. He cites a 

 case in which a transudate was caused to be absorbed by injecting 

 into it a substance which decreased its surface tension. 



4. Excretion. 



Milk and bile have about the same osmotic pressure as the 

 blood, but urine is almost dry in some animals: it i- u-ually 

 In I M rtonic in man but may be hypotonie. 



Traube maintains that the surface tension of the normal urine 

 is alu r than that of the blood, and that thi- is the 



dri\ iii;^ Ion e in excretion. 



Houe\<r. ll<.licr and others suppose that tin- -iib-iam < -s to 

 1 may be formed into solid bodies in tin- tubule cells, 

 and ihroun out into the hi men. 



It' lipoid-iii-oluble dyes arc fed to frogs, granule- in tlu- -11- 

 ol (i-riain -i ^mrnts of the kidney tubule are staim-d \\iih them. 

 Tin- <l\i i- not tirst excreted by the glomeruli and then ab-orbed 

 from tin lumen by the tubule cells, for if the vena Jacol >-. mi, 

 which -ii|>|>lies the tubules, is ligatured, no staining occurs, al- 

 though the renal arteries still supply the glomernli. 



Ihi- -tained granules in the tubule cells are thrown out into 

 tin- lumen and pass into the bladder. The.-c granule- u-ually 

 di ol\ e to form a slimy substance in the urine, bin -ome oi them 

 max remain intact. 



The circulation in mammalian kidneys cannot In- controlled 

 in the- -aim- \\ay, but after intravenous injection . >f , ( certain 

 lipoid-in-olublc- dye, no stain may be detected in the \\all- o| 

 the glomeruli, although the tubule cells are staineil. The -tain 

 in the lumen does not appear above the level of the -tained tubule 

 ci'lls. In the excretion of carmine, it may be found in -ranule- 

 in the tubule cells and lumen, similar to those, found in frog's 

 kidtiex 3. 



h ha- been -upposed that urea is excreted by collecting in 

 the-e granule-, and passing out with them, but it would be e\en 

 sim;iK-r t> a--ume that some substance is excreted into the lumen, 

 \\hich combine- with urea and so lowers the concent ration of that 

 in solution, thus accelerating its excretion. 



The chief recommendation for the granules is their valve-like 



