BLOOD. 201 



greater than in the arterial blood, although, from our know- 

 ledge of the fact that fibrin is employed in the process of nu- 

 trition, we should have expected an opposite result. Hence 

 we are led to attribute the excess of fibrin to the consumption 

 of a large proportion of blood-corpuscles, a view which is con- 

 firmed by the circumstance that the venous blood in this in- 

 stance is poorer in blood-corpuscles than the arterial. 



The proportions are reversed in analysis 4, but whether 

 from opposite causes or not, I cannot decide. It is singular 

 that in both instances the quantity of albumen is greater in 

 the venous than in the arterial blood, since there can be no 

 doubt that this constituent is consumed in the nutrition of the 

 tissues, and that a portion of the changed plasma enters the 

 lymphatics. I do not see how this increase can be accounted 

 for, unless we assume, as I have previously done, that a portion 

 of the globulin of the blood-corpuscles is converted into albu- 

 men during their metamorphosis. 



In the present state of our knowledge regarding the meta- 

 morphosis of the blood, it is as difficult as it is hazardous to 

 attempt to explain the various causes upon which the differ- 

 ences between venous and arterial blood are founded. There 

 are, as I shall proceed to show, decided differences between 

 the blood of the renal arteries and veins, and between the blood 

 of the hepatic vein and of the vena portse; and yet, as has 

 been already shown, the differences between the blood of the 

 aorta and of the vena cava are very immaterial and trifling. 

 To produce this ultimate similarity, other changes (not yet 

 heeded by the physiologist) must have largely contributed. 



Properties of the blood of the vena portce ; — its comparison 



with arterial blood. 



The blood of the vena portse in horses (the only animals in 

 which I have examined it) is darker than ordinary venous 

 blood ; the difference of the tint is however so slight, as to be 

 observable only upon actual comparison. It coagulates more 

 slowly than ordinary arterial or venous blood ; the clot is less 

 firm, more of a gelatinous appearance, and falls to pieces if an 

 attempt be made to lift it. I analysed the blood of the vena 

 portai of the two horses already alluded to. If arterial, ordi- 

 nary venous, and vena portse blood are deprived of their fibrin 



