November 24, 1905.] 



SCIENCE. 



655 



the glomerular filtration. It would be 

 more nearly correct to say that this process 

 is inversely proportional to the filtration. 

 There is, therefore, the more abundant and 

 unconcentrated urine when the blood fiow 

 is more abundant, and, on the contrary, a 

 more scanty and concentrated urine when 

 the blood flow is scanty. 



The Ludwig theory, as you are aware, 

 is based chiefly on the directly evident de- 

 pendence of the urinary secretion on the 

 blood stream through the kidneys and on 

 the blood pressure, and in fact this con- 

 nection is a striking one. I will remind 

 you of the experiments of Goll, which were 

 conducted as long ago as the year 1854, in 

 which the tension in the vessels was low- 

 ered by vagus irritation or by bleeding, 

 or elevated by clamping the large vessels 

 of the extremities, in which the volume of 

 the urine rose and fell according to the 

 increased or diminished flow of blood 

 through the kidneys. 



Against the whole theory of Ludwig, 

 supported as it was on many other facts 

 and arguments, Heidenhain brought a 

 series of objections, of which the following 

 was especially impressive. If the human 

 blood holds about one tenth of one per cent, 

 of urea and if it be estimated that the daily 

 excretion averages about 30 grams of urea, 

 it would follow that on the smallest esti- 

 mate 30 liters of fluid must filter through 

 the kidneys in twenty- four hours, for which 

 about 28 liters of water must be reabsorbed. 

 But if, according to the calculation of 

 Heidenhain, not more than 130 litres of 

 blood pass through the kidneys in the 

 course of a day, it follows that according 

 to Ludwig 's view about one quarter of this 

 volume filters out — a condition which would 

 lead to a wholly impossible concentration 

 of the blood in the glomerulus. In addi- 

 tion to this objection was urged the un-^ 

 economical work involved in the resorption 



through the urinary tubules of such great 

 quantities of superfiuous water. But we 

 now know through the careful investiga- 

 tions of Tigerstedt that there flows through 

 the kidneys during a very moderate di- 

 uresis in one minute a quantity of blood 

 corresponding to 80-100 per cent, of their 

 weight, or, in other words, since the hu- 

 man kidneys weigh about 300 grams, these 

 organs are traversed by about 240-300 

 grams of blood in a minute, equivalent to 

 345^30 liters in twenty-four hours. Thus 

 it is only about one twelfth to one four- 

 teenth of the volume of blood and not one 

 fourth of its volume, that is expressed. 

 And so far as the chemical work of re- 

 sorption is concerned, it must be remem- 

 bered that the work of excreting 30 grams 

 of urea through the elective action of the 

 tubular epithelium from blo*od holding 

 only 0.1 per cent, of urea must be exactly 

 as great as the corresponding work of re- 

 sorption by the same cells — in order to con- 

 centrate a 0.1 per cent, blood filtrate to 

 1.5 per cent, of urea through the resorption 

 of water. Now Heidenhain endeavored to 

 demonstrate the specific secretory function 

 of the epithelia by means of injection of 

 coloring matters. He injected into the 

 veins of a rabbit a definite quantity of 

 sodium sulphindigotate and removed the 

 kidneys .after a certain period of time, in- 

 jected the vessels with alcohol and exam- 

 ined the structures histologically. He then 

 found under certain conditions that the 

 glomeruli were wholly free from coloring 

 matter; the epithelia of the tubules, on the 

 other hand, were colored. And he con- 

 cluded from this that the dye was not se- 

 creted from the glomerulus but was se- 

 creted by the tubules. And from these 

 observations Heidenhain made the infer- 

 ence that the epithelia of the tubules se- 

 crete also other constituents of the uri-t^e. 

 These experiments are so well known that 



