148 APPENDIX TO CHAPTER XIII. 



to the lungs, when it once more receives oxygen and 

 becomes bright red. 



Thus the pulmonary veins differ from all other veins 

 in containing arterial blood; and the pulmonary artery 

 and its branches, from all other arteries in containing 

 venous blood. The ancient anatomists accordingly named 

 the pulmonary artery, the arterious vein. 



In Fig. 39, the vessels which convey venous blood are 

 shaded. 



again. How do the pulmonary veins differ from all other veins ? 

 The pulmonary artery and its branches from all other arteries ? 



APPENDIX TO CHAPTER XIII. 



THE BLOOD. 



Many of the main facts pertaining to the structure and composition 

 of blood may be easily demonstrated as follows: 



1. Kill a frog with ether (p. 46); 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, with 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. 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 test tube; 

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

 dilution. 



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

 indicated, on a clean piece of glass. To prevent drying, cover by 

 inverting over the drop a small glass whose interior has been moist- 

 ened 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 



