SYNTHESIS OF THE CARBOHYDRATES. 23 



The necessary mineral salts the plant likewise obtains from the 

 soil. 



The question now arises : In what manner do plants effect the 

 synthesis of those complex chemical substances which go to form 

 their tissues from the simple bodies which serve as their food-stuffs ? 

 The kinetic energy which is necessary to effect these changes is, as 

 has been stated, derived from the sunlight and transformed into 

 potential energy by the chlorophyl. We should thus expect to find 

 in those parts in which this is present the origin of those final 

 products which we meet with in the tissues of the plant. These 

 products may be divided into three groups, and in the following 

 pages an attempt will be made to describe the manner in which 

 representatives of each are formed. I shall accordingly consider 

 the origin of the carbohydrates, the fats, albumins, and certain non- 

 albuminous, nitrogenous bodies, all of which are also found in the 

 animal body, and which represent the essential food-stuffs of the 

 animal world. In doing so, I am aware that I am trespassing to 

 a certain extent upon what will follow in subsequent chapters ; but 

 as I shall deal with the chemistry of animal life more exclusively 

 in the present work, it has been deemed best to consider briefly the 

 principal syntheses which are effected by plants before proceeding to 

 a more detailed study of the subject proper. 



Synthesis of the Carbohydrates. It has been pointed out 

 that during exposure of chlorophyl-bearing plants to sunlight 

 the carbon dioxide of the air is decomposed, with liberation of 

 oxygen. The volume of gas thus set free is equivalent to the 

 volume of carbon dioxide that is decomposed. At the same time a 

 reduction of water takes place, as is apparent from the observation 

 that a larger amount of hydrogen is found in the plant than is 

 necessary to form water with all of the oxygen that is present at the 

 same time. It thus follows that one-half of the oxygen per volume 

 must be derived from carbon dioxide, and the other from water, 

 according to the equation : 



2CO 2 + 2H 2 = 2r + 4O, 

 4 volumes. 4 volumes. 



in which r represents one atom of carbon, one atom of oxygen, and 

 two atoms of hydrogen, which have been retained by the plant. A 

 combination of these atoms in one molecule, however, would repre- 

 sent one molecule of formic aldehyde, CH 2 O. 



Bach suggests that percarbonic acid is first formed together with 

 water and carbon and that the percarbonic acid then yields carbon 

 dioxide and hydrogen peroxide, while from the carbon and water 

 formaldehyde is formed, according to the equations : 



3H 2 CO S = 2H 2 C0 4 -f H 2 -f C 



2H 2 CO 4 = 2CO 2 + 2H 2 O 2 = 2CO 2 -f 2H.,O + O a 



HoO4-C = COH.H. 



