BLOOD OF POETAL VEIX. S/ 



The differences in regard to colour between arterial and 

 venous blood are sometimes not to be observed. If blood 

 runs very slowly from an artery, as from the bottom of a 

 deep and devious wound, it is often as dark as venous 

 blood. In persons nearly asphyxiated also, and some- 

 times, under the influence of chloroform or ether, the 

 arterial blood becomes like the venous. In the foetus 

 also both kinds of blood are dark. But, in all these cases, 

 the dark blood becomes bright on exposure to the air. 

 Bernard has shown that venous blood returning from a gland 

 in active secretion is almost as bright as arterial blood. 



b. General Composition. The chief differences between 

 arterial and ordinary venous blood are these. Arterial 

 blood contains rather more fibrin, and rather less albumen 

 and fat. It coagulates somewhat more quickly. Also, it 

 contains more oxygen, and less carbonic acid. According 

 to Denis, the fibrin of venous blood differs from arterial, 

 in that when it is fresh, and has not been much exposed 

 to the air, it may be dissolved in a slightly heated solution 

 of nitrate of potassium. 



Some of thj veins, however, contain blood which differs 

 from the ordinary standard considerably. These are the 

 portal, the hepatic, and the splenic veins. 



Portal vein. The blood which the portal vein conveys 

 to the liver is supplied from two chief sources ; namely, 

 that in the gastric and mesenteric veins, which contains 

 the soluble elements of food absorbed from the stomach 

 and intestines during digestion, and that in the splenic 

 vein ; it must, therefore, combine the qualities of the 

 blood from each of these sources. 



The blood in the gastric and mesenteric veins will vary 

 much according to the stage of digestion and the nature 

 of the food taken, and can therefore be seldom exactly the 

 same. Spaaking generally, and without considering the 

 sugar, dextrine, and other soluble matters which may 

 have been absorbed from the alimentary canal, this blood 



