CUSHNTS THEORY 223 



due to the physiological activity of the tubules, whether 

 this takes the form of absorption or secretion. 



In Fig. 29 it is shown that when sodium sulphate is the 

 cause of diuresis the oxygen intake is greatly increased^ 

 evidence of work being done by the cells. In diuresis thus 

 caused the concentration of the dissolved substances in the 

 urine differs materially from their concentration in the 

 plasma. 



Cushny's Theory 



The most remarkable feature in the action of the kidney 

 is that the character of the secretion is influenced by the 

 composition of the blood. WHien from any cause the latter 

 is disturbed the kidney reacts in such a way as to restore 

 it to the normal. The urine is usually more concentrated 

 than the blood ; but it may be more dilute, as when large 

 quantities of water have been drunk. 



It follows, therefore, that no theory of renal function 

 is complete unless it takes into account the adaptive 

 nature of the mechanism. This point of view is upper- 

 most in the most modern theory of renal secretion — that 

 due to Cushny. Cushny accepts filtration as sufficient to 

 account for glomerular activity. He believes the glomer- 

 ular fluid to consist of plasma minus proteins. He regards 

 the function of the tubules as one of active absorption of 

 water and of substances in solution, the cotnposition of the 

 reabsorbed fluid being practically Ringer s solution, whatever 

 may be the composition of the blood or the urine. 



Cushny has arrived at this conclusion by a comparative 

 study of the concentration of the principal constituents 

 in blood and in urine. Some of the blood constituents, 

 e. g. dextrose, sodium and chlorides, only pass into the 

 urine when they have attained a certain concentration in 

 the blood. These he calls Threshold Bodies. Others, e. g. 

 urea and sulphates, appear in the urine when present only 

 in traces in the blood. These he calls No-Threshold 

 Bodies. In between these groups are Intermediate Bodies 



