considered from some specud points of view. 421 



supposition might not be absolutely absurd, as we must as- 

 sume something of the same kind in the case of crystals. But 

 at the assumption that the molecules of any chemical com- 

 pound stand in a definite relation to the spiral form of the shell 

 of Cornuspira planorhis or of the fossil Nummulina radiata^ 

 every " thinking " naturalist would certainly shake his head. 



In connexion with the first appearance of life, Hackel lays 

 great stress on the artificial preparation of organic compounds. 

 Hitherto, however, no one has prepared hydrates of carbon 

 and albuminates from their elements ; and, with respect to 

 the artificial preparation of urea, formic acid, and other 

 retrogressive products of the animal organism, there was never 

 really any cause for making so much fuss about it. The ex- 

 pired carbonic acid is also a retrogressive product ; and this had 

 long been prepared artificially. The chemical processes which 

 take place in organic bodies seem much rather to speak in 

 favoui- of the assumption of special forces. 



Let any vegetable be planted in pin-e siliceous sand con- 

 taining as nourishment for it only carbonic acid, ammonia, 

 and the necessary inorganic salts. Let the whole be kept at 

 a temperature of about 68° F., and covered with a glass vessel 

 which is always kept at a scarcely higher temperature. The 

 plant and the soil in which it grows therefore receive light 

 and heat from without. Let us now see what becomes of 

 these two agents. 



If we bum hydrates of carbon in oxygen, two things take 

 place : — 



1. Separation of the carbon from the water of the hydi'ate 

 of carbon ; 2, combination of the carbon with the oxygen. 

 At the same time heat is always evolved. 



In the above plant the direct opposite of this takes place. 

 Under the influence of light the oxygen of carbonic acid sepa- 

 rates from the carbon, and the latter combines with water to 

 form hydrate of carbon. During this, heat, or, at any rate, 

 mechanical motion (in the form of light and heat) must neces- 

 sarily disappear. 



If, then, the plant be allowed to grow, say, through a whole 

 summer, and the hydrates of carbon produced be then burnt, 

 carbonic acid and water are again formed. A portion of the 

 heat manifested during this process can then be converted 

 into mechanical work, whilst another part passes over to 

 bodies Avhich are at least at a temperature of 68° F., and by 

 this means the products of combustion again acquire this 

 original temperatui-e. 



Now this whole process seems to stand in contradiction to 

 the second principle of the mechanical theory of heat, or to 



