160 Life and Health 



Experiment 70. Place on a glass slide a thin layer of defibrinated 

 blood (see Experiment 62); try to read printed matter through it. 

 This cannot be done. 



Experiment 71. Wash away the coloring matter from the twigs 

 (see Experiment 62) with a stream of water until the fibrin becomes 

 quite white. It is fibrous and elastic. Stretch some of the fibers to 

 show their extensibility; on freeing them, they regain their elasticity. 



Experiment 72. Take some of the serum saved from Experiment 62 

 and note that it does not coagulate spontaneously. Boil a little in a 

 test tube over a spirit lamp, and the albumen will coagulate. 



Experiment 73. To illustrate some of the phenomena of cir- 

 culation. Take a common rubber bulb syringe, of any standard 

 make. Attach a piece of rubber tube about six or eight feet long to 

 the delivery end of the syringe. 



To represent in a very crude way the resistance made by the 

 capillaries to the flow of blood, slip the large end of a common 

 glass medicine dropper into the outer end of the rubber tube. This 

 dropper has one end tapered to a fine point. 



Place the syringe flat, without kinks or bends, on a desk or table 

 Press the bulb slowly and regularly. The water is thus pumped into 

 the tube in an intermittent manner, and yet it is forced out of the 

 tapering end of the glass tube in a steady flow. 



Experiment 74. Take off the tapering glass tube, or, in the place 

 of one long piece of rubber tube, substitute several pieces of glass 

 tubing connected together by short pieces of rubber tubes. The 

 obstacle to the flow has thus been greatly lessened, and the water 

 flows out in intermittent jets to correspond to the compression of 

 the bulb. 



Experiment 75. By injecting with a syringe warm liquid gelatin 

 (colored red) into the aorta of a dead animal, the whole vascular 

 system can be filled. The gelatin sets solid when it becomes cold, 

 and by cutting up the organs into thin slices and examining these 

 under the microscope, the network of blood vessels can be most 

 clearly observed. HILL'S Manual of Human Physiology. 



