59O THE BOOK OF THE DOG. 



the blood to flow backwards, this would result in the opening of the valves, which would dam 

 the way and prevent the retrograde flow. 



The position of these valves in the veins of the forearm of a lean person can be distinctly 

 perceived by performing a very simple experiment. The arm is bared, a handkerchief is tied 

 tightly round it above the elbow, to stop the upward flow of blood. If the hand be then tightly 

 clenched, and the eye cast along the distended veins, we see a series of little knots here and 

 there. These represent the valves or pouches opened to prevent the backward flow of the blood. 



Now, these valves themselves are sometimes the seat of disorder ; from undue strain upon 

 them they get dilated and ruptured, and are therefore not in a position to perform their duties. 

 The veins themselves get elongated and tortuous, a state in which you frequently find them in 

 the limbs of old London cab-horses, and, more rarely, in the limbs of dogs as well, such as 

 Greyhounds. 



Let us now say a few words about the blood itself and its component parts. Blood is 

 composed of red particles, and a transparent fluid called the liquor sanguinis. If we allow blood 

 that has been newly drawn from an animal to stand for some time in a basin, we will perceive 

 that it resolves itself into two parts, viz., a red clot in the centre, not unlike a piece of raw 

 liver, and a pale straw-coloured transparent fluid, which is all around and above it. The clear 

 fluid is the serum of the blood, the clot is termed the crassainentum, this last consisting of the 

 red corpuscles of the blood. These latter, which seen under the microscope look like small 

 round discs or pieces of money, in the veins float along in liquor sanguinis. Chemically 

 examined, the red corpuscles are found to consist of what is called globulin, and also of 

 hcematin. Globulin is somewhat akin to albumen, while the hcematin it is which gives the 

 colour to the blood. This hcematin is a compound of carbon and iron. This latter fact gives 

 medical men a hint which we are not slow to act upon ; we know that in any animal in a 

 low state of health the red blood corpuscles are too few, and we know that animals that 

 breathe the largest amount of oxygen have the best and reddest blood are the healthiest and 

 happiest hence we give to ansemic patients good nutritious food, and iron in some shape 

 (that which is the most easily assimilated is the best) and recommend plenty of fresh air. 



The principal uses of the red corpuscles are two. They take oxygen (the life-giver) from 

 the air that is breathed, and they roll it away through the arteries to the capillaries ; then they 

 come back rolling their way along the veins laden with carbonic acid to the lungs, and there 

 give up their charge, which is exhaled. Busy bees are those red corpuscles, clustering around 

 the cell walls of the lungs, unloading their carbonic acid, and taking in oxygen with every 

 breath we breathe, then hurrying off again to perform the work for which the great Author 

 ordained them. 



Not less important is the work which the liquor sanguinis has to perform in the system. 

 The microscope reveals nothing of its composition, as it is within the body ; but when the 

 blcod is drawn, and placed in a basin, we find that, as we have already said, it separates into 

 clot and serum. This serum is a part of the liquor sanguinis ; the other part is the fibrin, 

 which, from the tendency its particles have to draw together or agglutinate, entangles the red 

 corpuscles, and thus the clot is formed. The serum itself is found to consist of water and 

 albumen, with various salts and other substances. It is from this albumen that the greater 

 portion of the tissues supply their waste. We find, then, in the blood not only the materials 

 of which the whole animal structure is built up, but those also which keep up the heat without 

 which life would be impossible. And whence does the blood get its own supply ? From the 

 food eaten and from the air breathed : and this surely tells its own tale. 



