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 Avith 

 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 aiTanging 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 vitahty ; 

 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 

 aflinities. 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 diff'erent 

 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 to this grand functioa of living plants, the following facts 

 Iseem the most important that have been ascertained. 



