CHAPTER VI 

 CIRCULATION OF THE NUTRIENTS 



I. Composition of the Blood 



149. Food and blood. — Thus far in our laboratory 

 studies we have tested various foods, and have found that 

 they all consist of one or more of the nutrients ; namely, 

 proteins, fats, carbohydrates {i.e. starch and sugar), fats, 

 mineral matters, and water. We have discussed the way 

 in which each of these nutrients is digested, and thus made 

 ready for absorption into the blood — for until the nutrients 

 actually become a part of blood, they cannot be of use to 

 the body. In 7 we described the red and white corpuscles 

 of the blood * (Fig. 5) and there stated that the liquid part of 

 blood is known as blood plasma. 



150. Composition of blood plasma. — Blood plasma con- 

 tains a large amount of water in which are dissolved the 

 various nutrients obtained by absorption from the alimentary 

 canal. The presence of each of these nutrients has been 

 demonstrated by applying the various food tests given in 

 23-28, "Plant Biology." Following is the percentage of 

 each nutrient found in the human body: — 



Water 90+ per cent 



Proteins S"*" per cent 



Fats, grape sugar, mineral matters . . . . 2~ per cent 



^ For a laboratory study of blood, see Peabody's " Laboratory 

 Exercises," pp. 50-53. 



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