20 PHOTOSYNTHESIS 



listing the interest of chemists in the subject of photosynthesis and the 

 slow progress which has been made in arriving at a clearer understandmg 

 of the chemical reactions involved. 



In certain respects the present has its points of similarity with the time 

 of Wohler and Liebig. Through the exhaustive studies of the nutritional 

 requirements of animals it has been found that besides the materials which 

 supply energy for the maintenance of bodily activity, the nitrogenous 

 materials necessary for the building of tissue and the mineral nutrients, 

 there are certain essential accessory factors which, as it were, serve to 

 maintain the "spark of life." These substances called vitamines have been 

 variously classified according to their origin, solubility in various solvents 

 and their specific action in preventing certain pathological conditions and 

 stimulating particular functions of the body. The vitamines from the 

 chemical viewpoint have proven to be highly elusive substances and their 

 presence can be determined only from the effects which certain materials 

 exert on various functions of the animal organism. Thus far it has not 

 been possible to synthesize vitamines or substances which play a similar 

 role or to prepare any mixtures which produce the same efi'ects as do these 

 substances. It appears, therefore, that we are dealing with substances 

 which can be produced only by the activity of the living plant. The sources 

 are not confined to the chlorophyllous plants ; yeasts have been found to 

 contain certain vitamines. However, the chlorophyll-bearmg plants not 

 only are a direct source of vitamines. but as the ultimate source of all food 

 material must be considered as of fundamental importance in the produc- 

 tion of all vitamines in nature. From a nutritional viewpoint, therefore, 

 at present it seems that we shall have to depend upon the natural photo- 

 synthetic process for the production of man's food supply on account of 

 the essential vitamines which can be supplied in no other manner. This 

 is quite aside from the many practical difficulties which any scheme for 

 the artificial production of foods entails. Such schemes must still be re- 

 garded as the fanciful dreams of the popularization of science. 



The more obvious significance, however, of the phenomenon of photo- 

 synthesis centers about the supplying of our earth with energy. 



2. Sunlight: the Prime-mover of CiviHzation i 



Our early progenitors were at some period of their development most 

 of them sun-worshipers, regarding the sun as that from which all bless- 

 ings flow. The human mind has wandered far in its groping for funda- 

 mental truth and has constructed for itself many divers gods and idols. 

 Scientific investigation is showing that the instincts of our sun-worshiping 

 forefathers were well founded. The sun is in fact the source of all our 

 material wealth, our power, our life. The full realization of this fact 

 has been very slow in penetrating our minds. 



Numerous have been the attempts to differentiate and classify peoples, 

 to ascribe the success of one group or the failure of another in meeting 



