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FAMILIAR LETTERS OS CHEMISTRY. 



regulate it. In our ordinary time-pieces, we know with mathematical accuracy the 

 effect produced on their rate of going, by changes in the length of the pendulum, 

 or in the external temperature. Few, however, have a clear concep^n of the 

 influence of air and temperature on the health of the human body ; and yet the 

 research into the conditions necessary to keep it in the normal state, is not more 

 difficult than in the case of a clock. 



LETTER VIII. 



MY DEAR SIR : 



Having attempted in my last letter to explain to you the simple and admirable 

 office subserved by the oxygen of the atmosphere in its combination with carbon in 

 the animal body, I will now proceed to present you with some remarks upon those 

 materials which sustain its mechanisms in motion, and keep up their various func- 

 tions namely, the Aliments. 



If the increase of mass in an animal body, the development and reproduction of 



its organs depend upon the blood, then those substances only which are capable of 



being converted into blood can be properly regarded as nourishment. In order 



I then to ascertain what parts of our food are nutritious, we must compare the com- 



I position of the blood with the composition of the various articles taken as food. 



Two substances require especial consideration as the chief ingredients of the 

 blood ; one of these separates immediately from the blood when it is withdrawn 

 from the circulation. 



It is well known that in this case blood coagulates, and separates into a yellowish 

 liquid, the serum of the blood, and a gelatinous mass, which adheres to a rod or 

 Btick in soft, elastic fibres, when coagulating blood is briskly stirred. This is the 

 fibrine of the blood, which is identical in all its properties with muscular fibre, 

 when the latter is purified from all foreign matters. 



The second principal ingredient of the blood is contained in the serum, and gives 

 to this liquid all the properties of the white of eggs, with which it is indeed iden- 

 tical. When heated, it coagulates into a white elastic mass, and the coagulating 

 substance is called albumen. 



Fibrine and albumen, the chief ingredients of blood, contain, in all, seven che- 

 mical elements, among which nitrogen, phosphorus, and sulphur, are found. They 

 contain also the earth of bones. The serum retains in solution sea salt and other 

 salts of potash and soda, in which the acids are carbonic, phosphoric, and sulphu- 

 ric acids. The globules of the blood contain fibrine and albumen, along with a red 

 coloring matter, in which iron is a constant element. Beside these, the blood con- 

 tains certain fatty bodies in small quantity, which differ from ordinary fats in 

 several of their properties. 



Chemical analysis has led to the remarkable result, that fibrine and albumen 



contain the same organic elements united in the samejgroportion that is, that 



/they are isomeric, their chemical composition the proportion of their ultimate 



( elements being identical. But the difference of their external properties shows 



that the particles of which they are composed are arranged in a different order. 



(See ante, page 16.) 



This conclusion has lately been beautifully confirmed by a distinguished physio- 

 logist (D6nis), who has succeeded in converting fibrine into albumen ; that is, 

 in giving it the solubility, and coagulability, by heat, which characterize the white 

 of eggs. 



Fibrine and albumen, beside having the same composition, agree also in this, 

 that both dissolve in concentrated muriatic acid, yielding a solution of an intense 

 purple color. This solution, whether made with fibrine or albumen, has the very 

 same reactions with all substances yet tried. 



Both albumen and fibrine, in the process of nutrition, are capable of being con- 

 verted into muscular fibre, and muscular fibre is capable of being reconverted into 

 blood. These facts have long been established by physiologists, and chemistry has 

 merely proved that these metamorphoses can be accomplished under the influence 

 of a certain force, without the aid of a third substance, or of its elements, and 

 without the addition of any foreign element, or the separation of any element pre- 

 viously present in these su' 



