1282 PHYSIOLOGY 



in its excretion, we must stop the glomerular transudate by some 

 means or other. This stoppage of the urinary flow can be effected in 

 two ways, viz. by section of the spinal cord in the neck, so as to 

 reduce the blood pressure to about 40 mm. Hg, i.e. below the minimum 

 necessary for the production of urine, or by cauterising portions of 

 the surface of the kidney by means of silver nitrate. If the 

 indigo be injected into the veins, after section of the cord, and 

 the animal be killed half an hour later, and the kidneys fixed 

 with absolute alcohol, they are found to be of a bright blue 

 colour, although no urine has been secreted. On cutting into the 

 kidneys the colour is seen to be confined to the cortex, and on making 

 microscopic sections granules of the pigment are found within the 

 lumen and in the epithelial cells of the convoluted tubules. If the 

 kidneys have been cauterised, the stain is confined to the convoluted 

 tubules of the cortex only under those areas which have been cauterised, 

 and where the glomerular functions have been abolished. It has been 

 suggested that the appearances after the injection of indigo are due, 

 not to the secretion, but to the absorption of water in the convoluted 

 tubules. A certain amount of the dyestuff is thus rendered visible 

 by becoming more concentrated, and is precipitated in a granular form, 

 as soon as the salt concentration of the fluid reaches a certain height. 

 The fact that these appearances are wanting after the injection of 

 ordinary carmine, which stains the glomeruli as well as the tubules, 

 combined with the histological facts mentioned in the last para- 

 graph, render this a somewhat forced explanation ; and we must take 

 the results of the injection of indigo-carmine as telling rather in favour 

 of a secretory than of an absorptive function on the part of the con- 

 voluted tubules. 



The question as to the secretory activity of the kidney can be 

 attacked from another side. The glomerular filtrate can contain only 

 those crystalloids of the blood which are diffusible and are not closely 

 combined with its colloidal constituents. Lowi has shown that in this 

 connection a contrast is to be drawn between the behaviour of sub- 

 stances, such as urea or sodium chloride, and certain other constituents 

 of the blood such as phosphates or sugar. Any increase in the rate at 

 which the glomerular secretion takes place must cause a corresponding 

 increase in the total amount of the solid diffusible constituents of the 

 blood-plasma which are turned out within a given time. Thus every 

 diuresis increases the total output of chlorides and of urea. On the 

 other hand, a diuresis caused, for example, by drinking large quantities 

 of water does not increase the total output of phosphates in a given 

 time, nor does it increase the very small amount of sugar which is 

 normally excreted by the kidneys. If, however, sodium phosphate be 

 previously injected into the blood, then any diuresis increases the 



