Proceedings of the British Association. 565 



change of matter in the tissues of his body, and thereby of making 

 hunger more endurable. Nor can he withstand the captivation of 

 brandy, which, acting as an element of respiration, puts a stop to the 

 change of matter, by performing the function which properly belongs 

 to the products of the metamorphosed tissues. The third part of 

 Prof. Liebig's Report treats of the recondite laws of the phenomena 

 of motion. As it is principally of a speculative character, we can 

 pass this over. The Professor concludes his communication by two 

 chapters : one on the theory of disease ; the other on the theory of 

 respiration. The whole life of animals consists of a conflict between 

 chemical forces and the vital powers. In the normal state of the body 

 of an adult, both stand in equilibrium. Every mechanical or chemical 

 agency which disturbs the restoration of this equilibrium is a cause 

 of disease. Disease occurs when the resistance offered by the vital 

 force is weaker than the acting cause of disturbance. Death is that 

 condition in which chemical or mechanical powers gain the ascendancy, 

 and all resistance on the part of the vital force ceases. Every abnor- 

 mal condition of supply or waste may be called disease. It is evident 

 that one and the same cause of disease — that is, of disturbance — will 

 have different effects, according to the period of life. A cause of 

 disease, added to the cause of waste, may in old age annihilate the 

 resistance of the vital powers, or, in other words, occasion death ; 

 while, in the adult state, it may produce only a disproportion between 

 supply and waste ; and in infancy only an abstract state of health, i. e. 

 an equilibrium between supply and waste. Prof. Liebig argues, from 

 what has preceded, that a deficiency of resistance in a living part to the 

 cause of waste is in fact a deficiency of resistance to the action of the 

 oxygen of the atmosphere. The Professor's theory may be compared 

 to a self-regulating steam-engine. The body, in regard to the produc- 

 tion of heat and of force, acts just like one of those machines. With 

 the lowering of the external temperature, the respiratition becomes 

 deeper and more frequent; oxygen is supplied in greater quantity, 

 and of greater density ; the change of matter is increased, and more 

 food must be supplied, if the temperature of the body is to remain 

 unchanged. It has been proved, that iron is not necessary to the 

 colouring matter of the blood, but that it forms an essential constituent 

 of blood globules. These globules, it is well known, take no part 

 in nutrition. Prof. Liebig conceives, that the iron is the great means 

 of conveying to the lungs the carbonic acid formed in the system ; 

 and he has made a calculation, that the iron contained in the body 



