1074 EXCRETION 



tion of the blood, or by furthering the activity of the renal cells. Con- 

 sequently, either the glomerulus or the tubule may be involved in this 

 process. Thus, we might say that digitalis enhances the circulatory 

 conditions, because it stimulates the cardiac musculature and raises 

 the tonicity of the vascular channels. Caffeine possesses a similar 

 action.^ It is evident, however, that a mere increase in the vascularity 

 or a passive injection of the renal capillaries does not give rise to a flow 

 of urine. Another way in which the secretory conditions might be 

 altered, is to change the osmotic pressure of the blood. For example, 

 if a hypertonic solution of sodium chlorid is injected into the circula- 

 tory system, the osmotic pressure of the blood is increased, and fluid 

 is drawn into the vascular channels from the lymphatics until 

 it acquires a lower osmotic pressure. ^ This condition is called 

 hydremic plethora. It follows then that the renal blood flow is more 

 rapid and forceful, a change which greatly favors the transudation 

 of the excess of fluid through the renal capillaries. The same effect 

 may be produced intentionally by the ingestion of large quantities 

 of water or by means of dialyzable substances, such as sodium sul- 

 phate, sodium or potassium bicarbonate, the acetate, citrate or bitar- 

 trate of potassium, liquor ammonii acetatis, liquor ferri et ammonii 

 acetatis, urea, and dextrose. The most efficient of these are the 

 bicarbonates and potassium acetate. Urea and dextrose may act 

 chiefly as direct stimulants to the renal cells, but also, in a measure, 

 by changing the osmotic conditions. Pituitary extract seems to 

 possess a direct action upon the cells although its action upon the 

 circulatory system cannot be excluded. 



A more detailed explanation of diuresis cannot be given unless re- 

 sort is taken to the well-conceived but still hypothetical absorption 

 ''theory. '^ If the polyuria of diabetes mellitus is taken as an example, 

 it might be said that the kidney is quite unable to concentrate the 

 urine against the concentrated sugar-urine in the tubules. In accord- 

 ance with the preceding discussion, this would imply that sugar be- 

 comes a ''non-threshold" substance, owing to the presence of sugar 

 in the blood in amounts greater than the optimum. 



Albuminuria. — While the proteins of the blood do not enter the 

 blood under normal conditions, their escape cannot be prevented if 

 the permeability of the glomerulus is increased. A condition of this 

 kind develops in acute nephritis and cardiac failure. The quantity 

 of the urine is then usually diminished, but the question of whether 

 this disease remains confined to the glomeruU or also involves the 

 tubules, cannot be decided with certainty. Theoretically, however, 

 we might expect to obtain a glomerular as well as a tubular nephritis. 

 In the chronic type of this disease the urine retains a low specific 

 gravity and viscosity^ and, using the absorption hypothesis as a basis, 



1 Lowi, Arch, fiir exp. Path, und Pharm., liii, 1905, i. 



2 Gottlieb and Magnus, ibid., xlv, 1901, 223. 



3 Burton-Opitz and Dinegar, Am. Jour, of Physiol., xlvii, 1918, 220. 



