152 WHAT DOES MAN LIVE UPON? 



years. The length of time and the extent of the area, 

 remove all those objections which may readily be made to 

 experiments on a small scale. Boussingault allowed those 

 four hectares to be cultivated in the usual Alsatian manner 

 during twenty-one years of the inquiry. But the manure 

 which was used was carefully weighed, as well as all that 

 which was each year harvested, and the quantity of carbon, 

 hydrogen, oxygen, nitrogen and ash of both, were always 

 accurately ascertained by chemical examination. The result 

 of these experiments was that, on an average, the annual 

 harvest gained from the soil, twice as much nitrogen, three 

 times as much carbon and hydrogen, and four times as 

 much oxygen, as had been given to it in manure presup- 

 posing here that the whole contents of the manure enter 

 the plants, which is in reality not the case. 



Since then carbonic acid, ammonia and water form the 

 food of plants, and we find that these matters never can be 

 so combined as not to contain far more oxygen than the 

 substances occurring in plants, free oxygen gas must neces- 

 sarily be set free in the vital processes of vegetables. 



And thus, as the final result of our inquiry, we arrive 

 at the following grand view of the interchange of matter 

 between the three kingdoms of Nature. Decomposition 

 and the process of respiration set free all vegetable and 

 animal substances (diminishing the amount of oxygen in 

 the air), in the form of carbonic acid, ammonia and water, 

 which diffuse themselves in the atmosphere. The plant 

 takes possession of these substances, and forms from them, 

 accompanied by an incessant increase of the oxygen of the 

 atmosphere, compounds rich in carbon and hydrogen, but 

 devoid of nitrogen, such as starch, gum, sugar and the 

 various fatty matters, and others rich in nitrogen, namely 

 albumen, fibrine and caseine. These compounds are for 



