1913.] 



Experiments on the Kidneys of the Frog. 



357 



chloride between § and 2 per cent, of pure NaCl showed a probable error 

 of + - 02 per cent. NaCl in such solutions. The actual figures given in 

 the communication must be considered as having that degree of error. 

 Although other salts, as KC1, CaCl 2 , were used, the amounts taken were too 

 small to introduce any appreciable error on this account. Since the solutions 

 used were very nearly solutions of one single chemical substance, the 

 refractometer readings, like specific gravity, give the molecular concentration 

 of the solution. 



3. Histological. — Immediately after each experiment the kidneys were 

 removed and placed in a fixing solution. This was generally alcohol, but in 

 some cases formalin (10 per cent.) and in others Flemming's fluid was used. 

 After being hardened the kidneys were embedded in paraffin and a series of 

 sections was taken from the middle of each kidney. When the blood-vessels 

 had been perfused with a mercuric salt and ammonium sulphide the sections 

 were mounted unstained. In other cases stains were used, generally 

 hasmatoxjdin and eosin. In one case complete serial sections were made of 

 the pair of kidneys. 



Injections of the blood-vessels were also made as described below and 

 serial sections prepared. 



Results. 



Histological. — The validity and significance of most of the experiments to 

 be described rests upon the proof that the whole of the capillary network 

 round the tubules normally receives blood both from the efferent vessels of 

 the glomeruli (that is, by way of the arterial system) and from the renal 

 portal vein. In order to demonstrate this we have injected a number of 

 kidneys on the one hand from the aorta, after ligature of the renal portal 

 veins, and on the other hand from the renal portal veins after occlusion of 

 the arterial circulation. The injections were made from a perfusion bottle 

 under a pressure approximately equivalent to the normal blood-pressure in 

 the frog's kidney, namely 20-24 cm. of water for the arterial perfusion and 

 10-12 cm. of water for the venous perfusion. In all the experiments the 

 venous outflow was unobstructed. The fluids used consisted of (a) Berlin 

 blue and (b) carminate of ammonia in Einger's solution. A few double 

 injections were made, carmine by the arteries and Berlin blue by the renal 

 portal vein. One gelatin double injection was also made, but in this case the 

 pressure used was obtained by means of an injection syringe and pressure 

 bottle and was higher than usual. It was found that whether the single 

 injection was made by the artery or by the renal portal vein the whole of 

 the intertubular capillary network appeared to be injected. In the case of 

 the double injections the glomeruli and efferent vessels were filled with the 



