186 
lieeig's organic chemistry. 
from the soil, will soon cease to nourish when the supply 
becomes deficient, and another crop, requiring less or none 
of this element, will flourish on the same soil. If the field 
be allowed to produce weeds, which will return to the soil, 
by decay, all that they have taken up, or if plants are pro- 
duced which do not abstract the alkalies, then the result of 
the slow disintegration of the soil again produces fertility 
by rendering the alkalies soluble. In connection with this 
point, it is to be considered that experiments have positively 
proven that roots expel those matters which the plant is not 
capable of assimilating, and the accumulation of these secre- 
tions ultimately proves injurious to the kind by which they 
have been secreted. These excrements, by gradual decom- 
position, become converted into humus, and cease to be 
hurtful, and even before decomposition may not be deleteri- 
ous to plants of a different nature. 
Very important observations follow on the character, for- 
mation, and operation of manures, and their peculiar value, 
together with extensive analyses of soil from different parts, 
for which we must refer to the work itself, and pass to the 
consideration of the second part, or the Application of Or- 
ganic Chemistry to Physiology and Pathology. 
" In order to keep up the phenomena of life in animals, 
certain matters are required — parts of organisms, which we 
call nourishment. In consequence of a series of alterations, 
they serve either for the increase of the mass ( nutrition,) 
or the supply of the matter consumed ( reproduction,) or, 
finally, for the production of force." 
The author considers that the state of rest is determined 
by the force of chemical affinity operating to effect combina- 
tion, and the subsequent motion, the result of a series of 
changes produced by the decomposition of the food itself, 
or the organs formed from it. In support of this opinion, 
the continued action of the oxygen of the atmospheric air 
first attracts his attention. The amount of this element, 
which is abstracted from the air by the lungs of a healthy 
