ON ORGANIC CHEMISTRY. 53 



where the piston-rod is to be raised, contains a stop-cock of a peculiar con- 

 struction, through which the steam must pass. By an arrangement connected 

 with the regulating-wheel, this stop-cock opens when the wheel moves slower, 

 and shuts when it moves more rapidly than is necessary to produce a uniform 

 motion. When it opens, more force (steam) is admitted, and the motion of 

 the machine is accelerated. When the stop-cock shuts, the steam is more or 

 less cut off, the force in the cylinder diminishes, the tension of the steam or 

 force increases, and is preserved for subsequent use. The force, that is, the 

 tension of the vapour, is produced by the change of matter by the combustion 

 of coals. The force increases with the temperature of the fire-place. There 

 are in these engines other arrangements, all intended for regulation. When 

 the force augments beyond a certain point, the channels for the admission of 

 air close themselves, combustion is diminished, and less force generated ; 

 but when the engine goes slower more steam is admitted to the cylinder, its 

 tension decreases, the air-passages are opened, and the cause of the disen- 

 gagement of heat, that is, of the production of force, increases. Another 

 arrangement supplies the fire-place incessantly with coals, in proportion as 

 they are wanted. 



The body, in regard to the production of heat and of force (in Liebig's 

 view), acts just like one of those machines. With the lowering of the external 

 temperature, the respiration 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. Liebig proves that iron 

 is contained in a state of protoxide in venous, and in the state of sesquioxide 

 in arterial blood. The latter very readily yields its oxygen to organic matter, 

 the former becomes very readily oxidized ; but the sesquioxide, in yielding 

 its oxygen to organic tissues, produces carbonic acid, which (according to 

 well-known facts) protoxide of iron readily absorbs. The globules of blood 

 darken when exposed to carbonic acid gas, but become florid when exposed 

 to oxygen, whilst all the carbonic acid is again evolved. Therefore,, the or- 

 ganic compound of iron which exists in venous blood, recovers in the lungs 

 the oxygen which it had lost, and liberates its carbonic acid. Professor 

 Liebig conceives that the iron is therefore the great means of conveying to 

 the lungs the carbonic acid formed in the system ; and he has made a calcu- 

 lation of how much the iron contained in the body could thus actually con- 

 vey, and the result of the calculation shows that twice as much carbonic acid 

 could thus be conveyed as actually is expelled daily from the system. 



In conclusion, I entreat that this abstract may not be regarded as doing 

 justice to Professor Liebig. It is difficult indeed to abstract from a work in 

 which every sentence contains some new views, if possible, more interesting 

 and more important than those preceding. And when the very unfavour- 

 able circumstances under which this abstract was prepared are considered, 

 I am sure that justice will be done to my learned friend by consulting the 

 report itself. 



In the opinion of all, Liebig may be considered a benefactor to his species, 

 for the interesting discoveries in agriculture published by him in the first 

 part of this report. And having in that pointed out means by which the food 

 of the human race may be increased, in the work now before us he follows 

 up the chain in its continuation, and shows how that food may best be 

 adapted to the nutrition of man. Surely there are no two subjects more 



