Proceedings of the British Association. 559 



motion and sensation are destroyed ; and the most energetic volition is 

 incapable of exerting any influence on the contractions of the heart, 

 on the motion of the intestines, or on the process of secretion. All 

 parts of the animal body are produced from the fluid circulating within 

 its organism, by virtue of vitality, which resides in every organ. A 

 destruction of the animal body is constantly proceeding. Every motion, 

 every manifestation of force, is the result of the transformation of 

 the structure, or of its substance. Every conception, every mental af- 

 fection, is followed by changes in the chemical nature of the secreted 

 fluids. Every thought, every sensation, is accompanied by a change in 

 the composition of the substance of the brain. It is to supply the waste 

 thus produced that food is necessary. Food is either applied in the 

 increase of the mass of a structure (that is, in nutrition), or it is appli- 

 ed in the replacement of a structure wasted (that is, in reproduction). 

 The primary condition for the existence of life is the reception and 

 assimilation of food. But there is another condition equally impor- 

 tant — the continual absorption of oxygen from the atmosphere. All 

 vital activity results from the mutual action of the oxygen of the 

 atmosphere and the elements of the food. All changes in matter 

 proceeding in the body are essentially chemical, although they are not 

 unfrequently increased or diminished in intensity by the vital force. 

 The influence of poisons and remedial agents on the animal economy 

 proves, that the chemical combinations and decompositions proceeding 

 therein, and which manifest themselves in the phenomena of vitality, 

 may be influenced by bodies having a well-defined chemical action. 

 Vitality is the ruling agent by which the chemical powers are made to 

 subserve its purposes ; but the acting forces are chemical. It is 

 from this view and no other, that we ought to view vitality. According 

 to Lavoisier, an adult man takes into his system, every year, 837 lb. of 

 oxygen, and yet he does not increase in weight. What, then, becomes 

 of the enormous quantity of oxygen introduced in the course of the 

 year into the human system ? The carbon and hydrogen of certain parts 

 of the body have entered into combination with the oxygen introduced 

 through the lungs and through the skin, and have been given out 

 in the form of carbonic acid, and the vapour of water. At every moment, 

 with every expiration, parts of the body are thus removed, and are 

 emitted into the atmosphere. No part of the oxygen inspired is again 

 expired as such. Now it is found that an adult inspires 32| oz. of oxy- 

 gen daily. This will convert the carbon of 24 lb. of blood into carbonic 

 acid. He must, therefore, take as much nutriment as will supply this 

 daily loss ; and, in fact, it is found that he does so ; for the average 



