TH1 i \« i;i i [ON ->i i i;i\i .".IT 



pens thai the urine excreted has a concentration of salts less than thai 

 presenl in the fluid of the blood. Some investigators believe thai Buch a 

 condition is possible only on the assumption thai water is activ< 

 creted, but a more plausible explanation based on the modern th< 

 is that the water thai is absorbed from the alimentary trad the 



kidney as a dilute saline solution, and is rapidly filtered off in a form 

 somewhal more dilute than the optima] solution which blood plasma musl 

 have for the well-being of the tissues. The tubules reabsorb the amounts 

 of water and <»t' those Baits, such as chlorides, uric acid, and sugar, nec- 

 essary to restore the plasma to the optimal concentration, bul <lo not 

 absorb the nonthreshold substances, such ;i^ un 



It is impossible to analyze the forces 'hat are responsible for such a 

 degree of absorption by the epithelium of the tubules. For the : 

 we must classify them, for want of a better term, as vital forces. Tim 

 questions that await immediate investigation are whether absorpl 



actually takes place, and, if il does BO, what factors cause it to vary. 



Many attempts have been made, by destroying the capsules or • 

 tubules by menus of poisons or by operation, to determine directly 

 indirectly the question of the function of the tubule 



In such experiments, however, the number of factors involved con- 

 fuse the issue and make the results practically valueless so far as de- 

 termining the normal functi f the tubules. Other experimenl 



have attempted to show absorption in the tubules by injecting diffusible 



substai s, such as chemicals and dyes, into the ureter under what they 



deemed sufficienl pressure to force the solution into the tubules, and by 

 an examination of the 1 » 1 < »< »< 1 or the tissues to determine whether or 

 the injected substances had hen absorbed. The results obtained by 

 this method are not convincing, probably chiefly because of the difficulty 

 in reaching the tubules, [ndeed, it is very questionable whether it is 

 possible to inject a substance into the tubules from the ureter. 



Fears ago ETeidenhain, tie exponent of the vital theory of excretion. 

 believed that he had demonstrated the ability of the renal cells to 

 crete dye Bubstances injected intravenously, since he failed to find 

 evidence of dye excretion in the capsule, bul found mass< [ye in the 



tubules ami stained granules in the cells of the tubules, he concluded 

 that the cells of the tubules had the power to excrete 'he dye, ami from 



analogy he believed that the tubules must likewise excrete the w.'.- 

 and the various nrinary salts. Subsequenl work, hi failed 



t infirm his belief thai the capsule is no1 concerned in the ion 



of the dye, and it is as reasonable to explain the result* i speri 



ments with tin- dyes l>} assuming that the n 



found in the tubules and in the cells are du< rption 



