NUTRITION. 145 



5 cc. water ; pour this into 95 cc. of boiling water, stirring as it enters. 

 With 25 cc. of this paste mix thoroughly 5 cc. of the filtrate (which con- 

 tains diastase extracted from the malt). Test a small portion of the 

 mixture at once for starch by adding a few drops of tincture of iodine, 

 and similar portions at intervals of half an hour until starch reaction 

 ceases. Taste the remaining paste. Into what has the starch been 

 converted ? 



F. Respiration. 



198. Destructive changes. — Coincident with the processes 

 which result in the formation of complex foods and from 

 them still more complex living protoplasm are those which 

 result in its destruction. In the green plants the construc- 

 tive changes predominate (because of extensive food making), 

 with the result that the plant accumulates additional organic 

 matter ; while in colorless plants destructive processes pre- 

 dominate, with the result that the plant increases in bulk, but 

 only at the expense of organic materials previously existent. 

 In all plants, however, both the constructive and destructive 

 changes go on at the same time and without conflict. 



199. Respiration. — A series of destructive changes is in- 

 cluded under the term respiration. It is a familiar fact that 

 the higher animals cannot live without a constant supply of 

 oxygen and a corresponding excretion of carbon dioxid. 

 This is not so generally known to be true of plants. It is, 

 nevertheless, true that no plant can live without a constant 

 supply of oxygen and a corresponding excretion of carbon 

 dioxid. The processes by which (a) oxygen is obtained, (b) 

 united with the living protoplasm, (c) this substance decom- 

 posed, and {d) carbon dioxid excreted constitute respiration. 



EXERCISE XXXIV. 



To show evolution of CO^ by respiration of seedlings. 

 Fill a wide-mouthed glass jar or bottle of I liter capacity one-third full 

 of peas and beans which have been swollen for a day in water, then 



