
THE PRINCIPLE OF VITAL AFFINITY. 183 
any part of the body communicate certain properties to the whole mass of blood 
which lies in contact with them, so as to modify or suspend for a long time the 
coagulation of such blood ;—that the blood which enters the vessels of any part 
where inflammation has been excited, has peculiar properties impressed on it, 
and even changes on its composition effected, merely by coming in contact with 
the portions of vessels where that process is going on, and with the portions of 
blood previously subjected to it ;—that the exudation from inflamed vessels ac- 
quires peculiar properties from the contact with the living surface on which it 
lies, first arranging itself as an organized structure, and then selecting and appro- 
priating, from the neighbouring bloodvessels, those materials by which it is assi- 
milated to the texture with which it is connected ;—again, that, in the sound 
state, every portion of matter which is deposited from the bloodvessels, to form 
part of a muscle or of a nerve, immediately acquires the peculiar vital properties 
of the part which it nourishes; and, in the case of muscles, even that the change 
produced in a portion of a fibre by the application of a stimulus, is instantly com- 
municated to the whole length of that fibre, and to many adjoining fibres. It 
appears to be nearly in the same manner that every portion of carbon and water 
which enters into the composition of any living vegetable cell, acquires the power 
of exerting the same vital affinities as actuated the matter which it replaces, or 
to which it is added. 
IV. Another principle, at least equally important and characteristic, may be 
stated in regard to this communication of vital properties to the materials which 
are added to living bodies, viz., That such powers are imparted only for a brief 
period of time, and that long before the time of the death of the structure to 
which they belong, all those materials lose the vital properties which have been 
given to them; perhaps, as has been lately stated, as a consequence of the ex- 
ercise of their peculiar vital powers, perhaps merely as a general law of vitality ; 
but equally, whether the peculiar properties which they acquire in living bodies 
are of the nature of nervous actions, vital contractions or attractions, or vital 
affinities. But as this principle is best illustrated by reference to the phenomena 
of excretions, we delay doing more than merely enunciating it at present. 
Having so far considered the general nature of the chemical changes which 
are peculiar to living bodies, and the kind of apparatus provided by nature for 
carrying on these changes, we may next take a more special view of the different 
chemical changes themselves, beginning with the greatest and most fundamental 
of all, the formation of the amylaceous matters by vegetables, acting on the water 
and carbonic acid with which they are supplied, both in the liquid form by their 
roots, and in the gaseous form by their leaves,—and the consequent evolution of 
oxygen. In regard te this grand function of living plants, the following facts 
seem the most important that have been ascertained. 
