550 APPENDIX. 



by a network of vessels originating in the " vasa efferentia," and here 

 an endosmotic interchange seems so far probable, that the more 

 concentrated blood of the different vessels is necessarily brought 

 into contact with the thin urinary solution, from which it again 

 abstracts water, and thus leaves the urine more concentrated. 



Ludwig advances the following grounds, in addition to the 

 anatomical arrangement of the kidneys, in support of this view. 

 According to him, his view explains why the urine never exceeds a 

 certain degree of concentration ; why a rapidly secreted urine is 

 in general very much diluted, whilst urine which is more slowly 

 secreted, is generally more concentrated; why the amount of 

 urine increases as the quantity of the excretory matters of the blood 

 is augmented ; and finally, why no more fluid passes from the 

 kidneys, after the solid constituents of the urine have been excreted 

 in the kidney. 



As Ludwig's whole theory rests essentially on the difference in 

 the pressures of the blood, he has directed his attention to the 

 more thorough elucidation of the influence of this relation upon 

 the urinary secretion. Whilst Kierulf endeavoured, under his 

 direction, to ascertain the influence of the character of the blood, 

 especially its amount of water, Goll* made the mechanical ques- 

 tion the subject of a series of very admirable observations. From 

 his labours we may conclude with certainty, that the lateral pres- 

 sure in the r arterial system of the kidneys exerts a very important 

 influence on the urinary secretion. Thus, for instance, on irrita- 

 tion of the nervi vagi, as well as when the vascular system is 

 deficient in blood, that is to say, during conditions in which the 

 tension in the arterial system is diminished, the urinary secretion 

 was found to be very considerably diminished, whilst this secretion 

 was greatly augmented during an increased tension of the blood in 

 the arterial system, when this condition was induced by the tying 

 of some of the larger arteries. It was further shown, that in 

 addition to this well-attested influence of the pressure of the blood, 

 other causes exerted a modifying action on the amount of the 

 secretion. But as it was further proved, that even where the con- 

 stitution and pressure of the blood were the same, the excre- 

 tion of urine from the two kidneys was never parallel (for either the 

 right or the left kidney secreted more than the other), other rela- 

 tions, as for instance, the influence of the kidneys upon the 

 contractile fibres of the renal tissue, and the yet unknown relations of 



* Uebcr d. Einfluss cles Blutdrncks auf. d. Harnabsonderung. Inaug.-Abd. 

 der med. Fac. zu^Zurich vorgel. 1853. 



