C 46 ) 
contradiction, and ve do not profess to decide whére 
doctors disagree. 
V. Of stable yard manures, lime, marl and Zyp- 
sum, and their agency in vegetation. 
We have already said, that vegetables in the last 
stage of decomposition, yield a black or brown pow- 
der, which Mr. Davy calls “a peculiar extractive 
matter, of fertilizing quality,” and which the che- 
mists of France have denominated terreau. This ve- 
getable residuum is the simple mean employed by 
nature to re-establish that principle of fertility in the 
soil, which the wants of man and other animals are 
constantly drawing from it. Ht was first analysed 
by Hessenfratz, who found it to contain an oily, 
extractive and carbonaceous matter, charged with 
hydrogen; the acetates and benzoates of potash, 
lime and ammoniac ; the sulphates and muriates of 
potash, and a soapy substance, previously noticed 
by Bergman. Among other properties (and which 
shows its combustible character) is that of absorb- 
ing, from atmospheric air, its oxigen, and leaving it 
only azote. ‘This was discovered by Ingenhouse, 
who, with De Saussure and Braconnet, pursued the 
subject by many new and interesting experiments, 
the result of which is— 
1. That the oxigen thus absorbed, deprives the 
terreau of part of its carbon, which it renders solu- 
ble and converts into mucilage ; and, 
2. That the carbonic acid, formed in the process, 
combines with the mucilage, and with it is absorbed 
by the roots of plants. 
If we put a plant and a quantity of slacked 
