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Prof. T. G. Brodie. 



respective activities of the different parts of the renal apparatus, another 

 series of experiments was performed, in which the action of diuretics upon 

 animals whose blood-pressure had been lowered by section of the spinal cord 

 was tested. It was necessary to employ rabbits for these observations, since 

 in both the cat and the dog the blood-pressure remains high enough after 

 section of the cord to enable the kidney to secrete quite freely when a 

 diuretic is administered. In the rabbit the blood-pressure falls to about 

 30 mm. Hg, and even though we injected large doses of saline and other 

 diuretics we never obtained a single drop of urine from the kidneys. The 

 plan of experiment therefore was to excise one kidney some 10 to 20 minutes 

 after division of the spinal cord, then inject the diuretic to be studied, and 

 half-an-hour later to remove the other kidney. In this way evidence was 

 obtained indicating the point of action of various diuretics. Without going 

 into the results in detail, I may state that the glomerulus is excited to secrete 

 by most of the diuretics of the saline group. Thus activity was well marked 

 after sodium sulphate, urea, or dextrose ; it was excited also by caffeine, but 

 completely absent after phloridzin. In the tubules the results were equally 

 striking, especially in the case of phloridzin, and in a minor degree in the 

 case of caffeine. In no instance was a large lumen produced, and the external 

 diameters of the convoluted tubules were only slightly increased. The contents 

 of the lumen consisted of fairly large secretion droplets, the droplets being 

 enclosed in membranes which stained with Weigert's haernatoxylin, and fairly 

 well with eosin. These results were chiefly observed in the proximal con- 

 voluted tubule. With the low blood-pressure there was never the slightest 

 indication of any marked distension of the tubule in any part of its course. 

 The glomeruli were never found secreting very actively, but were always 

 found separated from the capsular epithelium by a distinct though small 

 accumulation of fluid. 



An examination of the embryology of the renal tubule bears out the views 

 I have expressed. Originally, the excreting apparatus was a long tubule 

 opening at one end into the body cavity, and at the other on to the surface. 

 This tubule was lined throughout by a ciliated epithelium, which provided 

 the necessary motor mechanism for the expulsion of the secretion. Later, the 

 glomerulus was developed from the dorsal wall of the body cavity and received 

 a large and important blood supply from the aorta. Possibly its original 

 function was to secrete a watery fluid into the body cavity, and this in some 

 way served the renal tubule. The arrangement of its vessels as large loops 

 projecting from the ccelomic wall, even at this early stage, tends to indicate 

 that it was employed as a means of raising the fluid pressure within the 



