CLARIFIED AND UNCLARIFIED SEWAGE. 511 



ment of certain parts of plants ; and 2ndly, we keep the 

 soil loose or open by ploughing, harrowing, hoeing, 

 digging, and the like, that the air and sun-heat may 

 freely enter the soil and render these manures readily 

 available. This embraces the theory and practice of 

 cultivation. Now, highly important as is the use of 

 appropriate manures to aid in the development of our 

 growing crops, as a cultivator I attach more importance 

 than is commonly attached to the physical conditions of 

 the soil, especially to keeping the surface loose and the 

 soil porous that the water may get away, and that the 

 air and sun-heat may follow wherever the water or clarified 

 sewage goes. The clarified sewage is food placed within 

 reach of the roots ; the presence of air renders this food 

 more plentiful, and the sun-heat stimulates the roots to 

 feed. The fertility of the soil is therefore largely in- 

 fluenced by the amount of air and heat which it contains. 

 This brings me to the principal objection which I have to 

 urge against putting sewage on the land in an unclarified 

 or sludgy state. I am free to admit that the sewage 

 clarifies in its passage downwards, presenting to the roots 

 the same food as if the sewage had been previously clari- 

 fied ; but the surface of the earth is thereby made to act 

 as a filter, and the physical conditions of the soil are 

 altered. The unclarified sewage in passing through the 

 soil has become clarified, but the pores of the soil are 

 more or less closed against the passage of air> and a solid 

 or half liquid glutinous mass rests on the surface of the 

 earth throwing back the sun-heat. The food is there, but 

 the stimulants of air and sun-heat are shut out or greatly 

 diminished, and the fertility of the soil is impaired in a 

 corresponding degree. Horticulturists know well the im- 

 portance of earth-heat, as many of their highest efforts 

 depend on it. The greatest authority on this subject 

 (Lindley in the Theory of Horticulture, p. 136) thus 

 alludes to it : 



" It may hence be considered an axiom in horticulture 



