The Blood and Lymph. 87 



courses, which have been named according to the desti- 

 nation, the set of blood vessels going to and returning 

 from the lungs constitute the pulmonary system, the 

 other set having the office of distributing the blood to 

 and collecting it from the rest of the body being termed 

 the systemic circulation. Two branches of the latter are, 

 the renal system, going to the kidneys, and the portal 

 system, going to the liver. The material carried is a 

 reddish liquid, known as the blood. If we draw some 

 blood and let it stand for a time it is found to separate 

 into a fluid serum and solid portion (clot). The serum 

 is a pale yellowish fluid, and the solid portion a deep red. 

 If the drawn blood is allowed to stand for a still longer 

 time, more fluid will] be noted, while the clot has grown 

 smaller. What causes clotting? The fibrin which is 

 formed in the blood. This can be shown by whipping 

 the blood with a bundle of twigs, which when withdrawn 

 from the blood show stringy threads (fibrin), which are 

 thus removed and clotting prevented. These fibrin 

 threads imprison in their meshes the blood cells (cor- 

 puscles) and thus form the clot, consequently if the fibrin 

 is removed no clotting takes place. Clotting (coagula- 

 tion) is hastened by («) moderate warmth, (6) rest, (c) 

 contact with foreign matter, (d) free access of air; it is 

 retarded by (a) cold, (&) contact with living tissues, (c) 

 imperfect aeration, etc. Blood is alkaline in reaction, 

 that from the arteries being red in color, that from 

 the veins being purplish, relatively speaking, arterial 

 (red) blood is pure, venous (purplish) blood impure. 

 The blood cells are of two kinds, red (discs) and 

 white (irregular in shape), the disc shaped ones 



