FAMILIAR LETTERS ON CHEMISTRY. 25 



If we now compare the composition of all organized parts with that of fibrine 

 and albumen, the following relations present themselves : 



All parts of the animal body which have a decided shape, which form parts of 

 organs, contain nitrogen. No part of an organ which possesses motion and life is 

 destitute of nitrogen ; all of them contain likewise carbon and the elements of 

 water ; the latter, however, in no case in the proportion to form water. 



The chief ingredients of the blood contain nearly seventeen per cent, of nitro- 

 gen, and from numerous analyses it appears that no part of an organ contains less 

 than seventeen per cent, of nitrogen. 



The most convincing experiments and observations have proved that the animal \ 

 body is absolutely ^incapable of producing an elementary body, such as carbon or \ 

 nitrogen, out of suBstandJWWhich do not contain it; and it obviously follows, that 

 all kinds of food fit for the production either of blood, or of cellular tissue, mem- 

 branes, skin, hair, muscular fibre, &c., must contain a certain amount of nitrogen, 

 because that element is essential to the composition of the above-named organs ; 

 because the organs cannot create it from the other elements presented to them ; 

 and, finally, because no nitrogen is absorbed from the atmosphere in the vital 

 process. 



The substance of the brain and nerves contains a large quantity of albumen, 

 fi: d, in addition to this, two peculiar fatty acids, distinguished from other fats by 

 containing phosphorus (phosphoric acid). One of these contains nitrogen (Fremy). 



Finally, water and common fat are those ingredients of the body which are des- 

 titute of nitrogen. Both are amorphous, or unorganized, and only so far take part 

 in the vital process as that their presence is required for the due performance of 

 the vital functions. The inorganic constituents of the body are iron, lime, mag- 

 nesia, common salt, and the alkalies. 



The nutritive process is seen in its simplest form in carnivorous animals. This 

 class of animals lives on the blood and flesh of the graminivora ; but this blood 

 and flesh are, in all their properties, identical with their own. Neither chemical 

 nor physiological differences can be discovered. 



The nutriment of carnivorous animals is derived originally from blood ; in their 

 stomach it becomes dissolved, and capable of reaching all other parts of the body ; 

 in its passage it is again converted into blood, and from this blood are reproduced 

 all those parts of their organization which have undergone change or metamor- 

 phosis. 



With the exception of hoofs, hair, feathers, and the earth of bones, every part of 

 the food of carnivorous animals is capable of assimilation. 



In a chemical sense, therefore, it may be said that a carnivorous animal, in sup- 

 porting the vital process, consumes itself. That which serves for its nutrition is i 

 identical with those parts of its organization which are to be renewed. 



The process of nutrition in graminivorous animals appears at first sight altogether 

 different. Their digestive 'organs are less simple, and their food consists of vegeta- 

 bles, the great mass of which contains but little nitrogen. 



From what substances, it may be asked, is the blood formed, by means of which 

 their organs are developed ? This question may be answered with certainty. 



Chemical researches have shown, that all such parts of vegetables as can afford 

 nutriment to animals contain certain constituents which are rich in nitrogen ; and 

 the most ordinary experience proves that animals require for their support and 

 nutrition less of these parts of plants in proportion as they abound in the nitro- 

 genized constituents. Animals cannot be fed on matters destitute of these nitro- 

 genized constituents. 



These important products of vegetation are especially abundant in the seeds of 

 the different kinds of grain, and of peas, beans, and lentils ; in the roots and the 

 juices of what are commonly called vegetables. They exist, however, in all plants, 

 without exception, and in every part of plants in larger or smaller quantity. 



These nitrogenized forms of nutriment in the vegetable kingdom may be reduced 1 

 to three substances, which are easily distinguished by their external characters. 

 Two of them are soluble in water, the third is insoluble. 



When the newly-expressed juices of vegetables are allowed to stand, a separation 

 takes place in a few minutes. A gelatinous precipitate, commonly of a green tinge, 

 is deposited, and this, when acted on by liquids which remove the coloring matter,, 

 leaves a grayish white substance, well known to druggists as the deposite from 

 vegetable juices. This is one of the nitrogenized compounds which serves for the 

 nutrition of animals, and has been named vegetable jibrine. The juice of grapes is 

 especially rich in this constituent, but it is most abundant in the seeds of wheat, 

 and of the cerealia generally. It may be obtained from wheat flour by a mecha- 

 nical operation, and in a state of tolerable purity ; it is then called gluten, but the 



