CIECULATION IN THE BLOOD-VESSELS. 337 



In young animals the circulation is more swift, and it 

 appears to be quicker in the female than the male. Accord- 

 ing to Vierordt, the average rapidity of the blood's flow in 

 any warm-blooded animal is measured by the time required 

 for from 26 to 28 beats of the pulse in that animal. As we 

 have before mentioned, the circulation is most rapid in the 

 arteries, and slowest in the capillary system. 



I have here borrowed from Dr Dalton a diagram of the cir- 

 culation, which he correctly says is not a simple process, but 

 made up' of many different circulations, going on simultane- 

 ously in different organs. He says : " It has been customary 

 to illustrate it, in diagram, by a double circle, or figure of 8, 

 of which the upper arc is used to indicate the pulmonary, the 

 lower the general circulation. This, however, gives but a 

 very imperfect idea of the entire circulation, as it really takes 

 place. It would be much more accurately represented by 

 such a diagram as that given in Fig. 115, in which its varia- 

 tions in different parts of the body are indicated in such a 

 manner as to show, in some degree, the complicated character 

 of its phenomena. The circulation is modified in these dif- 

 ferent parts, not only in its mechanism, but also in its rapidity 

 and quantity, and in the nutritive functions performed by the 

 blood. In one part, it stimulates the nervous centres and 

 the organs of special sense; in others it supplies the fluid 

 secretions, or the ingredients of the solid tissues. One portion, 

 in passing through the digestive apparatus, absorbs the 

 materials requisite for the nourishment of the body; another, 

 in circulating through the lungs, exhales the carbonic acid 

 which it has accumulated elsewhere, and absorbs the oxygen, 

 which is afterwards transported to distant tissues by the cur- 

 rent of arterial blood. The phenomena of the circulation are 

 even liable, as we have already seen, to periodical variations 

 in the same organ; increasing or diminishing in intensity 



z 



