ON THE FOOD OF PLANTS. 103 



the crassamentum, or clotted part of blood, left 

 to nature, was not beneficially operative, until 

 decomposed, and even then, was nothing equal 

 to the serum in its effects; and the difference 

 in the composition of those separate substances, 

 is, that serum contains one-fortieth of alkaline 

 salts, and the clot none. But if the clotted 

 part of blood be broken small, and well mixed 

 with three times its bulk of water, in which 

 potash, in the proportion of one-fortieth part 

 the weight of the blood, be dissolved ; the blood 

 will be reduced, and the liquid be rendered 

 equally effective as the serous part. And if 

 the clotted part be mixed with as much slacked 

 lime as will form it into a thick paste, it will dis- 

 solve, and be immediately applicable ; but is not 

 so immediately efficacious as the solution by salts. 

 It, however, must be remarked, that clotted blood, 

 mixed with quick lime, and left drying for a short 

 time, will not dissolve, and is rendered useless. 

 Mr. Kirwan, after describing the analysis be- 

 fore quoted, observes, " Hence we see on the 

 " last analysis, the only substances common to 

 " the growing vegetables, and the soils in 

 " which they grow, are, water, coal, different 

 " earths and salts ; these, therefore, are the true 

 " food of vegetables : to them we should also 

 " add fixed air, though by reason of its decompo- 



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