DIFFERENCES IX DIFFERENT VESSELS. xliii 



the other hand, the addition of a little water darkens the blood. According to Pro- 

 fessor Stokes, the corpuscles in the former case "lose water by exosmosis, and become 

 thereby highly refractive, in consequence of which a more copious reflexion takes 

 place at the common surface of the corpuscles and surrounding fluid. In the latter 

 case they gain water by endosmosis, which makes their refractive power more nearly 

 equal to that of the fluid in which they are contained, and the reflexion is conse- 

 quently diminished."* But the presence of serum or of saline matter is not indis- 

 pensable to the brightening, for although the clot when washed free from serum 

 scarcely if at all reddens on exposure to oxygen, yet it is found that the red matter 

 when squeezed out of the clot and dissolved in water, still becomes brighter and 

 clearer on exposure to oxygen, whilst the colour is darkened (and the solution 

 becomes turbid from deposition of globulin), on being shaken with carbonic acid. As 

 in this case the colouring matter is extracted from the corpuscles and is reddened by 

 oxygen without the presence of salts, it is plain that the difference of colour of arterial 

 and venous blood essentially depends, not on a difference in the figure or density 

 of the corpuscles, but on an alteration produced in their colouring substance by 

 oxidation and deoxidation, which alters its absorptive effect on the light. 



2. Composition. The arterial blood, so far as is known, is uniform in nature 

 throughout ; but in passing through the capillary vessels into the veins, whilst it 

 generally acquires the common characters of venous blood, it undergoes special 

 changes in its passage through particular organs, so that the blood of all veins is not 

 alike in quality. Thus the blood of the hepatic veins differs from that of the portal 

 vein, and both are in various respects different from what might be regarded as the 

 common venous blood, which is conveyed by the veins of the limbs, and of the 

 muscular and cutaneous parts of the body generally. Moreover, Bernard has shown 

 that the blood of veins returning from secreting glands differs according to the state 

 of functional activity of the organs. Whilst their function is in abeyance the blood 

 in their veins is dark, as usual, but when secretion is active, the blood, which then 

 also flows much more freely and abundantly, comes through from the arteries to the 

 veins with very little, if any, reduction of its arterial brightness ; it also retains 

 nearly the whole of its separable oxygen. 



Compared with blood from a cutaneous vein, arterial blood is found to contain a 

 very little more water (about five parts in 1000) and to have a somewhat lower specific 

 gravity. The arterial plasma yields more fibrin and coagulates more quickly; the 

 serum is said by Lehmann to contain less albumen and less fat, but more extractive 

 and a little more saline matter. According to the same authority, the corpuscles also 

 contain less fat, but relatively more hsematin and salts. Arterial blood yields more 

 oxygen gas, and less of both free and combined carbonic acid. 



Blood of the portal vein, compared with that of the jugular vein, is stated by 

 Lehmann to contain more water in proportion to solid matter, less fibrin and 

 albumen, more fat, extractive matter and salts. Its corpuscles are said to be richer 

 in haematin. 



In the blood of the splenic vein, as compared with that of the corresponding artery, 

 according to the observations of Funke, the red corpuscles are smaller, more 

 spheroidal in form, and more resistant to the destructive effects of water ; and when 

 they run together it is in rounded heaps, not in regular piles. Their cruor has a 

 marked tendency to form crystals. The pale corpuscles are vastly more numerous 

 than in the arterial blood, and some of them have a yellowish tint (as if in transition 

 to red disks). Granule-cells occur occasionally and sparingly, twice as large as the 

 pale corpuscles, but otherwise resembling them. The plasma is distinguished by its 

 poverty in fibrin. 



The blood of the hepatic veins shows, according to Lehmann's statement, the 

 following differences from that of the portal vein. It is richer in both red and pale 

 corpuscles, possibly from loss of water. The red corpuscles present the same pecu- 

 liarities of size, form, resistance to water, and mode of aggregation, as in the splenic 

 venous blood. They contain less fat and salts than in portal blood, less haematin, at 

 least less iron, but somewhat more extractive matter; the proportion of pale cor- 

 puscles to the red is increased. The plasma is more concentrated, but is deficient in 



* Proc. Royal Soc., vol. xiii. p. 362. 



