466 OF THE CIRCULATION OP THE BLOOD. 



water. With respect to the chemical nature of these crystals, and to the effect 

 of reagents upon them, Funke has made innumerable experiments, but without 

 being able to come to any positive results. 1 ED.] 



CHAPTER IX. 



OF THE CIRCULATION OF THE BLOOD. 



1. Of the Circulation in General. 



492. THE Circulation of nutritive fluid through the body has for its object, 

 on the one part, to convey to every portion of the organism the materials for its 

 growth and renovation, together with the supply of Oxygen which is requisite 

 for its vital actions, especially those of the Nervo-Muscular apparatus ; and at 

 the same time to carry off the particles which are set free by the disintegration 

 or " waste" of the tissues, and which are to be removed from the body by the 

 Excreting processes. Of these processes, the one most constantly in operation, 

 as well as most necessary for the maintenance of the purity of the blood, is the 

 extrication of Carbonic acid, through the Respiratory organs ; and this is made 

 subservient to the introduction of Oxygen into the system. In Man, as in other 

 Vertebrated animals, there is a regular and continuous movement of the nutri- 

 tive fluid through the sanguiferous vessels ; and upon the maintenance of this, 

 the activity of all parts of the organism is dependent. In common with Birds 

 and Mammals, again, Man has a Respiratory circulation entirely distinct from 

 the Systemic; all the blood which has returned from the body being transmitted 

 to the lungs, and being brought back to the heart again, before it is again sent 

 forth for the nourishment of the tissues and for the maintenance of their func- 

 tional activity. The heart is placed at the junction of these two distinct circu- 

 lations, which may be likened to the figure 8 ; and it may be said to be formed by 

 the fusion of two distinct organs, a "pulmonary" and a " systemic" heart; for 

 its right and left sides, which are respectively appropriated to these purposes, 

 have no direct communication with each other (in the perfect adult condition, at 

 least), and seem merely brought together for economy of material. 3 Each system 

 has its own set of Arteries or efferent vessels, and of Veins or afferent trunks ; 

 these communicate at their central extremity by the Heart, and at their peri- 

 pheral extremity by the Capillary vessels, which are nothing else than the 

 minutest ramifications of the two systems inosculating into a plexus ( 292). 

 Besides the systemic and pulmonary circulations, however, there is another 

 which is no less distinct, although it has not an impelling organ of its own. 

 This is the " portal" circulation, which is interposed between the venous trunks 

 of the abdominal viscera and the Vena Cava, for the purpose of distributing that 

 blood through the Liver, in which organ its newly-absorbed materials undergo 

 assimilation ( 472), whilst its excrementitious matters are separated by the 

 secreting process. The Vena Portse, which is formed by the convergence of the 

 gastric, intestinal, splenic, and pancreatic veins, subdivides again like an artery, 

 so as to form a capillary plexus which extends through the whole substance of 



1 American Journal of Med. Sciences, April, 1852. 



2 At an early period of foetal life, as in the permanent state of the Dugong, the heart is 

 so deeply cleft, from the apex towards the base, as almost to give the idea of two separate 

 organs. 



