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Messrs. Bainbridge, Collins, and Menzies. [Mar. 27? 



much more easily carried out in the male than in the female frog, and the 

 former were almost invariably used. Frequently the mesenteric artery was- 

 also ligatured in order to limit the extent of the perfusion. 



In the later experiments the aortse were exposed immediately above the 

 kidneys, the right was tied off, and a cannula was placed in the left ; the 

 mesenteric artery was ligatured. Cannulas were then placed in the vena 

 cava just above the renal veins, the inferior end of the anterior abdominal 

 vein (after tying off the legs) and the ureters. The testes were removed 

 by the cautery. The advantage of this method is that the perfusion is 

 practically confined to the kidneys, and the arterial pressure can be more 

 readily gauged and adjusted than in the earlier experiments. The arterial 

 perfusion through the aorta was made at a pressure of 20-24 cm. of water ; 

 the venous perfusion pressure varied from 10 to 14 cm. of water. 



Solutions Used. — The following perfusing fluids were used : (1) Normal 

 Einger's solution (NaCI - 65 per cent., KC1 0"02 per cent., CaCl 2 003 per 

 cent.) ; (2) Hypotonic or hypertonic solutions of sodium chloride containing 

 also potassium chloride - 02 per cent, and calcium chloride 003 per cent. 

 — these are subsequently termed hypotonic or hypertonic Einger's solution ; 

 (3) Hypotonic or hypertonic Einger's solution with the addition of 0*1 or 

 0*2 per cent, sodium sulphate (anhydrous). The solutions were fully 

 oxygenated and were filtered before being put into the perfusion bottle. 

 Frequently oxygen was also bubbled through the perfusing fluid in the 

 bottle. The perfusion bottles were provided with a Mariotte tube. 



2. Physical. — The greater part of the work which required analytical 

 determinations of the materials used was carried out by means of the 

 refractometer. The instrument used was of the Pulfrick type without, 

 water cooler. To enable the instrument to work with less than one drop 

 of liquid, a small flat bottom tube was placed in the refractometer cup. 

 Between the top of the prism and the bottom of the flat bottom tube there 

 was a thin film of the liquid tested ; in the tube was a little water with a 

 thermometer. As neither the Pulfrick angles nor the corresponding indices 

 convey much meaning in the present communication, all the results are 

 returned as having a refractive index equal to a solution of sodium chloride 

 of some special strength. As has been shown before,* the refractive index of 

 solutions is proportional to their concentration. The refractive index of 

 water on the particular instrument used is at 20° C. ± 1° = 67° 127' ± 0-8' 

 with a probable error of one determination of +0 - 65'. The value of NaCl 

 is 1' = 0-0443 per cent. NaCl, and the determinations of strength of sodium 



* B. Walter, 'Ann. Phys. Chem.,' vol. 38, p. 107; 'Journ. Chem. Soc.,' 1890, A, 

 p. 202. 



