48 REPORT — 1842. 



to blood only its form ; and further, that it is incapable of forming blood out 

 of other compounds which do not contain the chief ingredients of that fluid. 

 Liebig does not, indeed, maintain that other compounds may not be trans- 

 formed in the body, for we know that they are ; but that they cannot form 

 the blood, the starting-point of the series. 



Animal and vegetable life are therefore closely connected ; for the Jirst 

 substance capable of affording nutriment to animals is the last product of the 

 creative energy of vegetables. The seemingly miraculous, in the nutritive 

 power of vegetables, disappears in a great degree ; for the production of the 

 constituents of blood cannot appear more surprising than the occurrence of 

 the fat of beef and mutton in cocoa beans, of human fat in olive oil, of the prin- 

 cipal ingredient of butter in palm oil, and of horse fat and train-oil in certain 

 oily seeds. 



Whilst considerations such as these have led Liebig to these conclusions 

 regarding the increase of mass in animals, he has still to account for the use 

 of the substances in food, which are destitute of nitrogen, but which we 

 know are absolutely necessary to animal life. Such substances are starch, 

 sugar, gum and pectine. In all of these substances we find a great excess 

 of carbon, with oxygen and hydrogen in the same proportion as in water. 

 They therefore add an excess of carbon to the nitrogenized constituents of 

 food, and they cannot possibly be employed in the production of blood, be- 

 cause the nitrogenized compounds contained in the food already contain exactly 

 the amount of carbon which is required for the production of fibrine and 

 albumen. Liebig enters into proofs to show that very little of the excess of 

 this carbon is ever expelled from the system either in the form of solid or liquid 

 compounds. It must therefore be expelled in the gaseous state. In short, by 

 a train of admirable reasoning, he arrives at the interesting conclusion, that 

 they are solely expended in the production of animal heat, being converted by 

 the oxygen of the air into carbonic acid and water. The food of carnivorous 

 animals does not contain non-azotized matters, so that the carbon and hydro- 

 gen necessary for the production of animal heat are furnished in them from 

 the waste of their tissues. The transformed matters of the organs are ob- 

 viously unfit for the further nourishment of the body, that is, for the increase 

 or reproduction of the mass. They pass through the absorbent and lymph- 

 atic vessels into the veins, and their accumulation in these would soon put a 

 stop to the nutritive process, were it not that the blood has to pass through 

 a filtering apparatus, as it were, before reaching the heart. The venous 

 blood, before returning to the heart, is made to pass through the liver and 

 the kidneys, which separate from it all substances incapable of contributing 

 to nutrition. The new compounds containing the nitrogen of the transformed 

 organs, being utterly incapable of further application in the system, are ex- 

 pelled from the body. 



Those, again, which contain the carbon of the transformed tissues, are 

 collected in the gall-bladder as bile, a compound of soda, which being 

 mixible with water in every proportion, passes into the duodenum and 

 mixes with chyme. All the soda of the bile, and ninety-nine-hundredths of 

 the carbonaceous matter which it contains, retain the capacity of resorption 

 by the absorbents of the small and large intestines — a capacity which has 

 been proved by direct experiment. 



The globules of the blood, which in themselves can be shown to take no 

 share in the nutritive process, serve to transport the oxygen, which they give 

 up in their passage through the capillary vessels. Here the current of 

 oxygen meets with the carbonaceous substances of the transformed tissues, 

 and converts their carbon into carbonic acid, their hydrogen into water. 



