GLANDULAR SECRETIONS. 



91 



carried off in the respiratory process, to assist in the calorifying func- 

 tion. The bile, therefore, seems to be partly excrementitial, partly 

 recrementitial. 



The sources of the bile may be found in the disintegration of the 

 fibrinous and nervous tissues when the amount of food is just suf- 

 ficient to supply the waste of the system, the liver removing such 

 products as are rich in carbon and hydrogen ; and in any excess in 

 the non-azotised compounds derived from the food, beyond the amount 

 that is requisite for the supply of the respiratory process, or that 

 can be deposited as fat. In this elimination of hydro-carbon the 

 liver is subsidiary to the lungs. In the foetus it is the great decar- 

 bonizing agent. 



In regard to the kind of blood from which the bile is secreted, 

 analogy would point to the hepatic artery, although the experiments 

 of Kiernan seem to fix it upon that of the vena porlse. Both have 

 their supporters. Those who embrace the supposition of the secre- 

 tion from the hepatic artery^ assign to the vena portse the office of 

 mixing thoroughly with the blood heterogeneous substances absorbed 

 from the stomach and intestines, before transmitting them to the heart. 

 Those who contend for the secretion from the vena portae assign to 

 the hepatic artery the office of nourishing the liver, which from its 

 small size, in comparison with the vena portse, seems more justly to 

 be its function. 



Secretion of urine. — This secretion is purely excrementitial, being 

 destined to removed certain effete substances from the blood, whose 

 retention would be positively injurious. As it is the function of the 

 liver to remove the superfluous carbon, so it is of the kidney to get 

 rid of the excess of nitrogen in the blood. 



The kidney is a tubular gland, being 

 formed of uriniferous tubes, both convoluted 

 and straight, the convoluted being found in 

 the cortical portion, the straight in the me- 

 dullary. The cortical portion is the most 

 vascular, and it is probably the seat of the 

 greater part of the secreting process, whilst 

 the medullary is concerned in carrying the 

 secreted matter; the two parts being in this 

 respect analogous to the cortical and me- 

 dullary portions of the brain. 



In the cortical portion of the kidney are 

 seen a number of small dark points, called 

 corpora malpighiana ; each of these is com- 

 posed of a mass of minute blood-vessels very 



* Distribution of the renal vessels; from kidney of horse ; a, branch of renal artery, of, 

 afferent vessel; m, m, Malpighian tufts; e/, c/, efferent vessels; p, vascular plexus sur- 

 rounding the tube ; st, straight tube ; ct, convoluted tube. Magnified about 30 diam. 



Fig. 23. 



