v] THE SOURCES OF FOOD 139 



All writers who have considered the question of the 

 circulation of nitrogenous food-stuff in nature have 

 pointed out the remarkable scarcity of these com- 

 pounds. Everywhere in the land and sea organisms 

 suffer from a state of chronic nitrogen hunger, and 

 this incessant demand for more nitrogen food than 

 the sea or soil affords has led to a host of adaptations 

 of modes of nutrition. It has been suggested that life 

 first developed, or sprang into existence on the earth 

 in the presence of accumulations of amino-acids 

 formed after the crust of the earth first began to 

 solidify permanently. Ammonia is still given off in 

 the emanations from volcanoes and it may be that 

 plutonic activity, in the presence of conditions that 

 can never recur while the earth remains a planet, 

 gave rise to extensive accumulations of nitrogen 

 compounds capable of acting as the soil on which the 

 germs of life, introduced to the earth from outer 

 space, developed. One must suppose that such 

 nitrogen compounds were at one time more abundant 

 than they are now. 



If they were, then it is probable that the metabolism 

 of organisms was more wasteful than it is at the 

 present, just as the metabolism of putrefactive and 

 fermentative bacteria, organisms which live in a 

 greater plenitude of food than any others, are of all 

 the most wasteful. Such primitive organisms were 

 probably saprophytic in habit, that is they lived by 



