COAGULATION OF BLOOD 157 



drops of human blood in drops of saline of o . 6, 0.7, o . 8, o . 9, i , and i . i per 

 cent, examine every ten minutes under a high-power microscope. The 

 corpuscles of some of the slides will swell up and may disintegrate, others 

 will show crenation as in figure 126. In the isotonic solutions the corpuscles 

 w T ill appear of their normal size and condition. 



10. Coagulation of Blood. a. Normal Clot. Anesthetize a dog, 

 insert a cannula into the carotid or femoral artery, and draw samples of 

 blood into two or three clean, dry test-tubes. Draw one sample into a test- 

 tube that has had its sides oiled. Note the exact time at which the blood 

 was drawn into the test-tubes and set the test-tubes in a test-tube rack. Ex- 

 amine at intervals of 30 seconds by gently inclining the test tubes. Presently 



FIG. 132. Microscopic View of Clot Showing Fibrin Network. 



it will be noted that the blood becomes more viscous and does not flow freely 

 up the sides of the test-tubes. Later the whole mass will become jelly-like 

 and will retain the form of the test-tube. Note the time of the first slight 

 change, and also when the clot becomes more perfect. The sample in the 

 oiled test-tube will be found to clot more slowly. 



If the test-tubes of clotted blood are left standing for a day, the coagulum 

 will become similar in size and a transparent yellowish blood will make its 

 appearance on the surface or between the sides of the clot and the test-tube 

 wall. This fluid is the serum and it is squeezed out by the shrinking of 

 the fibrin which holds the corpuscles in its meshes. 



b. Microscopic Examination of the Process of Clotting. Take a drop of 

 fresh blood from the tip of your finger under sterile conditions and mount 

 on a microscopic slide in a few drops of salt solution, and examine immediately 



