232 THE BLOOD. 



variation. There are three grand divisions of the venous sys- 

 tem, which in a physiological point of view, are deserving of 

 particular notice. , 



1st. The pulmonary venous system, by which the dark or 

 venous blood, after it has been restored to its arterial hue is 

 returned again to the left ventricle of the heart, through the 

 pulmonary veins. Here we have the apparent anomaly, of 

 veins carrying arterial blood, an/1 of an artery the pulmonary, 

 which transmits venous. 



2d. The systemic venous system, or that of which the roots 

 are formed in the two venae cavae. 



3d. The portal venous system. In this we have the singular 

 instance of a vein which has its origin, like the rest, from 

 capillary branches, branching again like an artery, so as to form 

 a second set of capillary vessels in the substance of the liver, 

 from which arises a new venous trunk, called the hepatic 

 vein. If we except the placental circulation of the child, no 

 other instance of a similar distribution of the veins appears 

 in the human body. 



Of the Blood. 



The blood of a healthy person indicates a tendency to coag- 

 ulate very soon after it is discharged from the vessels which 

 naturally contain it, although it is perfectly fluid in those 

 vessels. 



If it remain at rest, after it is drawn from the vessels, it soon 

 coagulates into a solid mass, of a soft texture. From this solid 

 mass a fluid is soon observed to issue, which appears in very 

 small drops on almost every part of the surface. These drops 

 quickly increase and run together, and in a short time the fluid 

 surrounds the solid mass, and exceeds it in quantity. 



The solid part which thus appears upon the spontaneous 

 separation of the blood, is denominated Crassamentum or 

 Cruor ; the fluid part is called Serum. 



The substance which contains the red color of the blood 

 remains with the Crassamentum. The Serum, when it sepa- 

 rates without agitation, is free from the red color. 



