314 THE VITAL FUNCTIONS. 



tive object, and as to the nice adjustment of chemical 

 affinities which has been provided in order to ac- 

 complish the intended effects.* Electricity is, no 

 doubt, an important agent in all these processes ; 

 but in the absence of all certain knowledge as to 

 the mode in which it is excited and brought into 

 play in the living body, the chasm can for the 

 present be supplied only by remote conjecture.! 



The process which constitutes the ultimate stage 

 of nutrition, or the actual incorporation of the new 

 material with the solid substance of the body, of 

 which it is to form a part, is involved in equal 

 obscurity with that of secretion. 



Some light, indeed, has recently been thrown on 



* The only instance in which we can perceive a correspondence 

 between the chemical properties of the secretion, and the kind of 

 blood from'which it is prepared, is in the liver, which, unlike all the 

 other glands, has venous, instead of arterial blood, sent to it for that 

 purpose. The veins, which return the blood that has circulated 

 through the stomach, and other abdominal viscera, are collected into 

 a large trunk, called the vena portce, which enters the liver, and is 

 there again subdivided and ramified, as if it were an artery: its minuter 

 branches here unite with those of the hepatic artery, and ramify 

 through the minute lobules which compose the substance of the liver. 

 After the bile is secreted, and carried off by hepatic ducts, the re- 

 maining blood is conducted, by means of minute hepatic veins, 

 which occupy the centres of each lobule, into larger and larger 

 trunks, till they all unite in the vena cava, going directly to the heart. 

 (See Kiernan's Paper on the Anatomy and Physiology of the Liver, 

 Phil. Trans, for 1833, p. 711.) A similar system of venous ramifi- 

 cations, though on a much smaller scale, has been discovered by 

 Jacobson, in the kidneys of most fishes and reptiles, and even in 

 some birds. 



i' It appears, however, to be established by the researches of 

 Donne that there exi?t, both in plants and in animals, electric 

 currents, determined by the acid or alkaline quality of their fluids, 

 and being probably at the same time the chief source of these pro- 

 perties. Ann. Sc. Nat. serie 2, i. 125. 



