266 THE AMERICAN MONTHLY [Sept. 



be shown hereafter. In a little while (usually in 45 

 minutes from the beginning of the observation), the red 

 corpuscles begin to present the same phenomenon. 

 They escape in such numbers from the sharply defined 

 edges of the clot, that the liquid soon becomes so filled 

 with them that further microscopical examination is im- 

 possible. If the tube be now removed from the stage 

 and placed in a vertical position, in a short time the 

 corpuscles will fall to the bottom, leaving a clear space 

 above filled with serum. We might be disposed to con- 

 sider this the dissolution of the coagulum, but the ap- 

 pearance is deceptive, for if the contents of the tube be 

 forced out by the breath, the clot will be seen in the 

 form of a slender cord of fibrin floating in the liquid. 

 The clot is not dissolved, but the contraction of the net 

 work of fibrin makes the meshes too small to contain the 

 serum and the corpuscles at first imprisoned in the coagu- 

 lum." 



To Study the Net Work of Fibrin. — . . . .A drop of a 

 frog's or of a mammal's blood is placed on a slide and 

 left to coagulate in a moist chamber. When the blood 

 is so firm that it may be inverted without displacement, 

 immerse it in a vessel of filtered water. The blood will 

 soon be decolored ; remove the slide gently, and stain 

 with the iodine solution or with eosine. Cover and ex- 

 amine in the staining solution. Iodine preparations are 

 not permanent ; to preserve the eosine specimen run un- 

 der the cover a drop of salted glycerine colored with a 

 little eosine. Salted glycerine, which will preserve ani- 

 line stain for a long time, is made as follows : Shake to- 

 gether 40 grms. of glycerine with an excess of common 

 salt. Let it settle, then decant. . . . 



THE HEART. 



To study the cardiac muscle cells. — . . . .Dissociate these 

 in a fragment from a frog's auricle by the aid of the 40 

 per cent caustic potash solution. These preparations 



