258 BLOOD 



brownish green, or even black shade, when exposed to the air, and 

 becomes turbid from the deposition of very fine molecular granules. 

 It has a faint alkaline reaction, speedily develops ammonia on 

 exposure to the air, and coagulates on being boiled, as well as on the 

 addition of mineral acids or of a watery solution of iodine, into a 

 thick white mass, without any separation of serum. It is also ren- 

 dered turbid by water, and then resembles under the microscope a 

 finely granular mass in which long threads are plainly discernible. 

 Hydrochlorate of ammonia does not remove the turbidity, and the 

 caustic alkalies or acetic acid remove it only slightly. Dilute 

 acetic acid causes the fluid to gelatinize, and removes the blackish 

 green colour, if it had previously been induced by exposure to 

 the air. The caustic alkalies also convert the clear fluid into 

 a colourless, tenacious jelly. Sugar may sometimes, but not 

 always, be detected in this fluid. As caterpillars generate a larger 

 quantity of fat within a short period than any other animals, 

 their blood is i'lso the richest in fat; amounting in one experiment 

 to 27'5-g- of the solid residue. The fluid of the dorsal vessels in 

 insects does not appear to differ essentially from the above- 

 described juice, containing precisely the same elements with the 

 exception of those nucleated cells which resist the action of acetic 

 acid and the caustic alkalies. 



The blood of the arteries differs from that of the veins in con- 

 taining a smaller quantity of the solid constituents belonging to 

 the blood-cells, which however contain relatively more heematin 

 and salts than the cells of venous blood, but far less fat. The 

 intercellular fluid of the arterial blood is richer in fibrin than that 

 of venous blood. The serum of the former contains somewhat 

 more water, and consequently less albumen ; for if we compare 

 the solid constituents of the serum of both kinds of blood in 

 regard to their quantity of albumen, we shall find an equal amount 

 of this substance in each. The case is different with the fats, 

 extractive matters, and salts; for the first are considerably diminished 

 in the arterial fluid serum, and even in its solid residue; and while 

 the salts are but slightly augmented, the extractive matters are 

 considerably increased in quantity. The arterial blood moreover 

 contains relatively more free oxygen than the venous blood. 



The portal blood differs in constitution according to the different 

 stages of the digestive process ; during digestion, when drink, as well 

 as food, has been partaken of, it is rich in water and intercellular 

 fluid ; the number of blood-corpuscles is therefore small, the fibrin is 

 slightly, and the fat very considerably augmented, while the albu- 



