462 PHYSIOLOGY. 



urine are here secreted; negative, in that the serum-albumin of the 

 blood is prevented from passing through. 



In support of the part that blood-pressure bears to secretion it 

 has been noted that, when the total contents of the vascular appa- 

 ratus are increased so that blood-pressure also increases, there fol- 

 lows an increased secretion; that increased action of the heart 

 increases the amount of urine; and that variations in the caliber of 

 the renal artery give proportionate urinary secretions. 



The diuretics made use of by the physicians owe their efficiency 

 mainly to these principles. Digitalis increases the quantity of urine 

 by raising blood-pressure, whereas urea, potassium nitrate, caffeine, 

 etc., act upon the rodded epithelium of the tubuli contorti. 



It must not be forgotten that at all times there is glomerular 

 pressure by reason of the vasa efferentia being of smaller lumen than 

 that of the afferentia. 



Fig. 177. (STIRLING, after ROY.) (From Mills's "Animal Physiology," 

 copyright, 1889, by D. Appleton and Company.) 



Kidney curve, Curve of the volume of the kidney. T, Time-curve; intervals 

 indicate a quarter of a minute. A, Abscissa. 



Colheim and Eoy, in their experiments with the oncometer, have 

 noted that the curve representing the volume of the kidneys runs 

 parallel with the curve of arterial pressure; it has smaller oscilla- 

 tions, both respiratory and cardiac. The nervous influences acting 

 upon the renal secretion are vasomotor; existence of the so-called 

 secretory nerves has not yet been definitely demonstrated. 



Toxicity of the Urine. After the ablation of the two kidneys 

 the animal dies from uraemia; that is, there is an accumulation of 

 the urinary, products in the blood. The removal of one kidney is 

 not necessarily fatal. The urine of daytime is more toxic than that 

 at night; it is especially narcotic, while night urine is more con- 

 vulsivant. A man excretes enough poisonous material by the kid- 

 neys in two days to cause death. When there is an excess of urea 





