A STUDY OF THE BLOOD 121 



presence of each of these nutrients in the beef serum may 

 be demonstrated by applying the various tests given on 

 pp. 44_46. Thus, if a small portion of the serum be put 

 into a test tube and heated, it coagulates, showing that pro- 

 teids are present. The occurrence of mineral matters is 

 proven by the ash that is left after blood is burned. Grape 

 sugar and fats are likewise present, though in smaller 

 quantities than one would expect. Starch is, of course, 

 absent. 



Change in Blood on mixing with Oxygen. When the blood 

 passes through the lungs, as already stated, it absorbs oxy- 

 gen. The resulting change in color can be seen from the 

 following experiment. Pour a small amount of defibrinated 

 blood into a glass bottle and stopper tightly. When the 

 bottle is shaken vigorously, the blood is mixed with the oxy- 

 gen in the bottle, and the dark maroon color changes almost 

 instantly to a bright scarlet. The same change in color 

 takes place when the serum is poured off and the blood clot 

 is exposed to the air. 



3. HUMAN BLOOD 



Application of the Study of Beef -blood. All of the facts 

 learned from the preceding study of beef-blood are equally 

 true of human blood. As soon as it flows from the body, 

 the fibrinogen changes to fibrin, and thus a clot is formed. 

 Coagulation is of great practical importance, since it provides 

 a natural means of closing up injured blood vessels, and of 

 preventing loss of blood. 



Red Blood Corpuscles. The form and size of red blood 

 corpuscles have been already discussed in connection with 

 the study of the cellular structure of the body (see p. 26). 

 When highly magnified they appear as circular disks, the 

 color of which is not red, as one would expect, but yellowish. 

 The deep red color of the blood is due to the fact that every 

 drop contains such a countless number. 



Like other cells they are composed of protoplasm. Chemt 



