SYNTHESIS OF PROTEIN 19 



can be formed from carbohydrates is known, and Leathes states 

 that this action is exothermic, several molecules of simple sugar 

 going to the formation of one (larger) molecule of fat, having, of 

 course, a higher caloric value. The fat is almost exclusively 

 found in the fruit. 



Incidentally, energy is bound in the formation of proteins. 

 This energy comes indirectly from the sun. Atmospheric nitrogen 

 is fixed in a form available for plant use by certain bacteria. 

 Each gram of nitrogen so fixed carries with it a considerable 

 quantity of energy which is obtained from the oxidative decom- 

 position of 100 mg. mannitol, the parent alcohol of the carbo- 

 hydrate, mannose. 



To conclude, the plant acts as a transformer of kinetic into potential 

 energy by the formation of carbohydrates, fats, proteins (the so-called 

 proximate principles of food) and a few other substances of minor 

 importance as storehouses of energy. 



Having regard to the fact that free energy is of vital import- 

 ance, and that the potential energy of the foodstuffs is readily 

 rendered available, one would consider it a profitable study to 

 determine the exact mechanism of this conversion. So far, study 

 of pure chlorophyll has led to negative results. Kremann and 

 Schnidlerschitsch have recently shown that pure chlorophyll, in 

 alcohol, absorbed the same amount of CO 2 as the alcohol itself, 

 and it made no difference whether the solution were exposed to 

 light or kept in the dark. The absorption spectrum of neither 

 chlorophyll a nor chlorophyll b nor chlorophyll a +b is similar 

 to the spectrum of the living green leaf. Knowledge is incom- 

 plete both of the chemical nature of the various constituents of 

 the chloroplast and of the distribution and physical state of the 

 components of this heterogeneous system. The pigments are 

 associated with a colloid complex and the absorption of CO 2 

 with alterations in the electrical state. 



To sum up, man obtains the energy necessary for his main- 

 tenance and for the performance of physical work from the 

 disruption of proteins, carbohydrates and fats, synthesised in 

 the first instance by green plants which trap and store solar 

 energy. Historically and until quite recently, the energy of sun- 

 light, apart from an insignificant amount drawn from the tides, 

 was the sole income of energy available for the world. Mankind 

 still maintains himself solely on the energy derived from the 

 sun through the intermediary of plant and animal metabolism, 

 but he derives his energy for work to an increasing extent from 



