190 THE HUMAN BODY. 



APPENDIX TO CHAPTER XIII. 



Many of the main facts pertaining to the structure and composi- 

 tion of blood may be easily demonstrated as follows: 



1. Kill a frog with ether (note, p. 68); cut off its head, and collect 

 on a piece of glass a drop of the blood which flows out. Spread out 

 the drop so that it forms a thin layer. Hold the glass up against the 

 light, and examine the blood with a hand lens magnifying four or five 

 diameters. The corpuscles will be readily seen floating in the plasma. 



2. Wind tightly a piece of twine around the last joint of a finger; 

 then, taking a needle, prick the skin near the root of the nail. A 

 large drop of blood will exude. Spread it out on a piece of glass 

 and examine, as described above for frog's blood. The corpuscles 

 will be seen floating in the blood liquid, but not so easily as in frog's 

 blood, since those of man are considerably smaller. 



[3. If a compound microscope is available the form, size, and 

 color of human and frog red blood-corpuscles can be demonstrated; 

 also the tendency of the human to aggregate in rolls, and the color, 

 form, size, and relative number of the colorless corpuscles. As any 

 one possessing a compound microscope is sure to know how to 

 mount a specimen of blood for examination with it, or, if not, to 

 have at hand some treatise on the use of the microscope giving the 

 necessary information, details need not be given here.] 



4. Obtaining a large drop of human blood as above described (2) 

 note: a, that as it flows from the wound it is perfectly liquid; b, 

 that it is red and very opaque; c, spread it out very thin on the glass; 

 note that it then looks yellow when held over a sheet of white paper; 

 d, mix a similar drop with a teaspoonful of water in a wine glass; 

 note that the mixture is yellowish, or, if not, becomes so on further 

 dilution. 



5. Place another large drop of human blood, obtained as above 

 indicated, on a clean glass plate. To prevent drying up cover by 

 inverting over the drop a wine-glass whose interior has been moistened 

 with water. In four or five minutes remove the wine-glass and note 

 that the blood drop has set into a firm jelly. Replace the moist 

 wine glass, and in half an hour examine again. The blood will then 

 have separated into a tiny red clot, lying in nearly colorless serum. 



6. If a slaughter-house is accessible the clotting of blood may be 

 Still better illustrated. Provide two -large wide-necked glass bottles 

 and a bundle of twigs. When the butcher bleeds an animal collect 

 j ojjg bottle some blood, taking care that nothing else (contents of 



