104 THE BLOOD. 



223. SEPARATION OF THE CORPUSCLES FROM THE 

 SERUM. Add 30 cubic centimeters of a saturated solution 

 of sodium chlorid to 270 cubic centimeters of water, then 

 mix with it 30 cubic centimeters of blood, which has been 

 defibrinated by beating it while freshly drawn. Pour it 

 into a flat-bottomed, shallow dish and allow it to stand 

 until the corpuscles have settled. Decant the serum, and, 

 after mixing the corpuscles with more salt solution as be- 

 fore, allow to settle and decant again. By this means the 

 serum can be entirely removed. Preserve the first portion 

 of the solution for testing in Experiments 234, 236, and 

 237. If any of the corpuscles have been destroyed it may 

 be reddened. 



224. DETERMINATION OF THE SPECIFIC GRAVITY OF 

 BLOOD. Prepare a mixture of benzol and chloroform, of 

 which the specific gravity when tested with a sensitive 

 hydrometer shall be somewhat less than that of blood. 

 Into this mixture allow a drop of blood to fall. Freshly- 

 drawn blood for example, from the end of the finger is 

 best, though the method can be demonstrated by the use 

 of defibrinated blood. When the blood has sunk, add chlo- 

 roform, drop by drop, stirring meanwhile, until the drop 

 floats in the midst of the liquid; that is, it has the same 

 specific gravity. Then filter out the blood, covering the 

 funnel to prevent evaporation, and determine the specific 

 gravity of the mixture by means of a sensitive hydrometer. 

 The mixed liquids can be preserved for future tests. 



225. Wind a string around one of the fingers until it 

 is congested, then prick it at the root of the nail with a 

 needle or knife, sterilized by passing through a flame. 

 Test the reaction of the blood, using a piece of neutral, 

 glazed litmus-paper. After rinsing off the blood with a 

 little distilled water the paper is blue. 



