V.] THE BLOOD. 35 



thai there are no holes in it. If there are any fine pores, close 

 them with a little white of egg, and coagulate it with a hot iron. 



(/>.) After several hours observe that no haemoglobin has 

 passed into the water. 



(c.) Test the diifusate for chlorides (AgN0 3 + HN0 3 ). 



8. Phenomena of Coagulation. Decapitate a rat, and allow 

 the blood to flow into a small porcelain capsule. Within a few 

 minutes the blood congeals, and when the vessel is tilted the blood 

 no longer moves as a fluid, but as a solid. It then coagulates com- 

 pletely. Allow it to stand, and after an hour or so, pale-yellow 

 coloured drops of fluid the serum are seen on the surface, being 

 squeezed out of the red mass, the latter being the clot, which con- 

 sists of fibrin and the corpuscles. 



9. Formation of Clot and Serum. Draw out a glass tube into a fine 

 capillary pipette at both ends, leaving a bulb in the middle, and suck some 

 uncoagulated blood, either from one's finger or from the heart of a frog, into 

 it, seal up the ends of the tube, allow the blood to coagulate, and examine 

 the tube under a microscope. Observe the small red shrunken clot, and the 

 serum squeezed out of the latter. 



10. Frog's Blood Coagulation of the Plasma. Place 5 cc. of normal 

 saline (0.75 per cent, salt solution) in a test-tube surrounded with ice. 

 Expose the heart of a pithed frog, and open the ventricle, allowing the blood 

 as it escapes to flow into the normal saline. Mix, and the corpuscles (owing 

 to their greater specific gravity) after a time subside. After they have 

 subsided remove the supernatant fluid the plasma mixed with normal 

 saline by means of a pipette. Place it in a watch-glass, and observe that it 

 coagulates. 



11. Mammalian Blood. 



(A.) Study coagulated blood obtained from the slaughter-house. 

 Collect the blood of a sheep or ox in a perfectly dry cylindrical 

 vessel, and allow it to coagulate. Set it aside for two days, and 

 then observe the serum and the clot. Pour off the pale, straw- 

 coloured serum, and note the red clot, which has the shape of the 

 vessel, although it is smaller than the latter. 



(B.) If the blood of a horse can be obtained, study it, noting that the upper 

 layer of the clot is paler in colour ; this is the buffy coat. 



12. Circumstances Influencing Coagulation. 



Effect of Cold. Place a small platinum capsule a brass or glass thimble 

 will do quite well on a freezing mixture of ice and salt, decapitate a frog or 

 rat, and allow the blood to flow directly into the cooled vessel. At once it 

 becomes solid or congeals, but it is not coagulated. As soon as the blood 

 becomes solid, remove the thimble and thaw the blood by placing it on the 

 palm of the hand, when the blood becomes fluid, so that it can be poured into 

 a watch-glass ; if the vessel be once more placed on the freezing mixture, the 

 blood again congeals and solidifies, and on its being removed becomes fluid. 

 Observe at the same time that the colour and transparency of the blood are 



