HUMUS 67 



mental difference between the process occurring 

 when a wood match is burnt and that occurring when 

 a horse eats a meal of hay or corn. The only differ- 

 ences are that in the case of the match the energy is 

 delivered rapidly and in the form of light and heat, 

 while in the case of the horse it is delivered slowly 

 and is utilized for warmth, for locomotion, for per- 

 forming complex chemical reactions, and so forth. 

 In both cases the underlying principle obtains that 

 Carbon on being oxidized or degraded to form Carbon 

 dioxide yields energy. 



Looked on in a somewhat similar way the decaying 

 organic matter in the soil, or humus, may fairly be 

 considered as a unit substance, and the soil con- 

 taining it regarded as a storehouse of energy. From 

 time immemorial gardeners and farmers have recog- 

 nized its value. Under the dominating influence of 

 chemical ideals they ignored more or less completely 

 the energy factor, and regarded the manuring of the 

 crop as an act undertaken with a view of supplying 

 to the plant the chemical constituents of which it 

 stood in need. In so doing, of course, they tacitly 

 accepted the value of manure, both mineral and 

 other, as a source of energy for what else is food in 

 its varied forms ? but they focussed their attention 

 on constituents necessary for plant life, and only 

 emphasized energy considerations so far as the direct 

 utilization of the sun's rays by the leaves of the 

 plant were concerned. 



With the growing recognition of the importance 

 of bacteria, there has been in recent years a marked 

 increase in the attention paid to the nature and 



