LECTURE VI. 
OF MANURES OF VEGETABLE AND ANIMAL ORIGIN. OF 
THE MANNER IN WHICH THEY BECOME THE NOURISH- 
MENT OF THE PLANT. OF FERMENTATION AND PUTRE- 
FACTION. — OF THE DIFFERENT SPECIES OF MANURES OF 
VEGETABLE ORIGIN ; OF THE DIFFERENT SPECIES OF 
ANIMAL ORIGIN. OF MIXED MANURES. GENERAL 
PRINCIPLES WITH RESPECT TO THE USE AND APPLICA- 
TION OF SUCH MANURES. 
That certain vegetable and animal substances 
introduced into the soil accelerate vegetation and 
increase the produce of crops, is a fact known since 
the earliest period of agriculture ; but the manner 
in which manures act, the best modes of applying 
them, their relative value and durability, are still 
subjects of discussion. In this Lecture, I shall 
endeavour to lay down some settled principles on 
these objects ; they are capable of being materially 
elucidated by the recent discoveries in chemistry 5 
and I need not dwell on their great importance to 
farmers. 
The pores in the fibres of the roots of plants are 
so small, that it is with difficulty they can be 
discovered by the microscope ; it is not therefore 
probable, that solid substances can pass into them 
from the soil. I tried an experiment on this sub- 
ject: some impalpable powdered charcoal, procured 
by washing gunpowder, and dissipating the sulphur 
r 2 
