86 PRINCIPLES OF PHYSIOLOGY 



operations in the animal body. The proto- 

 plasm of the plant combines these with oxygen, 

 forming more complex chemical compounds. 

 Thus by means of chlorophyll, and under the 

 action of the energy of light, it decomposes the 

 carbonic acid of the air, retaining the carbon 

 and returning the oxygen to the air. The 

 carbon is then united with oxygen and hydro- 

 gen to form starchy substances, which, by the 

 action of an amylolytic ferment (diastase), may 

 be changed into sugars, In a similar way, the 

 ammoniacal bodies are used up to form pro- 

 teins. All this is done by the protoplasm of 

 the plant cell, and there can be little doubt that 

 the formation of these bodies is the result of 

 chemical operations in the protoplasm, which 

 is alive. To do this it must have oxygen, and 

 it must get rid of the waste body, carbonic acid. 

 This constitutes the true respiration of a plant, 

 and must not be confused with the chlorophyll 

 action above referred to. The plant thus 

 transforms the kinetic energy of the sun's 

 rays into the potential energy stored up 

 in the starch and in the protein matter 

 in its cells, Fats may also be formed. The 



