40 



ANIMAL CHEMISTRY. 



More especially in reference, to nitrogen, we 

 roust suppose that it is removed from the 

 stomach by some more direct means, and 

 not by the blood, which fluid must already, 

 in passing through the lungs, have become 

 saturated with that gas, that is, must have 

 absorbed a quantity of it, proportioned to its 

 s : Ivent power, like any other liquid. By the 

 respiratory motions, all the gases which rill 

 the otherwise empty spaces of the body are 

 urged towards the chest ; for by the motion 

 of the diaphragm and the expansion of the 

 chest a partial vacuum is produced, in con- 

 sequence of which air is forced into the 

 chest from all sides by the atmospheric pres- 

 sure. The equilibrum is, no doubt, restored, 

 for the most part, through the windpipe, but 

 all the gases in the body must, nevertheless, 

 receive an impulse towards the chest. In 

 birds and tortoises these arrangements are 

 reversed. If we assume that a man intro- 

 duces into the stomach in each minute only 

 |th of a cubic inch of air with the saliva, 

 this makes in eighteen hours 135 cubic 

 inches ; and if th be Deducted as oxygen, 

 there will still remain 108 cubic inches of 

 nitrogen, which occupy the space of 3 Ibs. 

 of water. Now whatever may be the actual 

 amount of the nitrogen- thus swallowed, it 

 is certain that the whole of it is given out 

 again by the mouth, nose, and skin ; and 

 when we consider the very large quantity 

 of nitrogen found in the intestines of exe- 

 cuted criminals by Magendie, as well as the 

 entire absence oif oxygen in these organs, 

 (26,) we must assume that air, and conse- 

 quently nitrogen, enters the stomach by re- 

 sorptipn through the skin, and is afterwards 

 exhaled by the lungs. 



When animals are made to respire in gases 

 containing no nitrogen, more of that gas 

 is exhaled, because in this case the nitrogen 

 within the body acts towards the external 

 space as if the latter were a vacuum. (See 

 Graham "On the Diffusion of Gases.") 



The differences in the amount of expired 

 nitrogen in different classes of animals are 

 thus easily explained ; the herbivora swal- 

 low with the saliva more air than the carni- 

 vora; they expire more nitrogen than the 

 latter, less when fasting than immediately 

 after taking food. 



13. In the same way as muscular fibre, 

 when separated from the body, communi- 

 cates the state of decomposition existing in 

 its elements to the peroxide of hydrogen, so 

 a certain product, arising by means of the 

 vital process, and in consequence of the 

 transposition of the elements of parts of the 

 stomach and of the other digestive organs, 

 while its own metamorphosis is accom- 

 plished in the stomach, acts on the food. 

 The insoluble matters become soluble they 

 are digested. 



It is certainly remarkable, that hard-boiled 

 white of egg, or fibrine, when rendered so- 

 luble by certain liquids, by organic acids, 

 or weak alkaline solutions, retain all their 

 properties except the solid form (cohesion) 



without the slightest change. Their ele- 

 mentary molecules, without doubt assume 

 a new arrangement ; they do not, however, 

 separate into two or more groups, but re- 

 main united together. 



The very same thing occurs in the di- 

 gestive process ; in the normal state, the food 

 only undergoes a change in its state of co- 

 hesion, becoming fluid without any other 

 change of properties. 



The greatest obstacle to forming a clear 

 conception of the nature of the digestive 

 process, which is here reckoned among 

 those chemical metamorphoses which have 

 been called fermentation and putrefaction, 

 consists in our' involuntary recollection of 

 the phenomena which accompany the fer- 

 mentation of sugar and of animal sub- 

 stances, (putrefaction,) which phenomena 

 we naturally associate with any similar 

 change; but there are numbe&less cases in 

 which a complete chemical metamorphosis 

 of the elements of a compound occurs with- 

 out the smallest disengagement of gas, and 

 it is chiefly these which must be borne in 

 mind, if we would acquire a clear and accu- 

 rate idea of the chemical notion or concep- 

 tion of the digestive process. 



All substances which can arrest the phe- 

 nomena of fermentation and putrefaction in 

 liquids, also arrest digestion when taken into 

 the stomach. The action of the empyreu- 

 matic matters in coffee and tobacco smoke, 

 of creosote, of mercurials, &c., &c., is on 

 this account worthy of peculiar attention 

 with reference to dietetics. 



The identity in composition of the chief 

 constituents of blood and of the nilrogenized 

 constituents of vegetable food has certainly 

 furnished, in an unexpected manner, an 

 explanation of the fact that putrefying hlood, 

 white of egg, flesh, and cheese produce the 

 same effects in a solution of sugar as yeast 

 or ferment; that sugar, in contact with these 

 substances, according to the particular stage 

 of decomposition in which the putrefying 

 matters may be, yields, at one time, alcohol 

 and carbonic acid ; at another, lactic acid, 

 mannite, and mucilage. The explanation 

 is simply this, that ferment, or yeast, is 

 nothing but vegetable fibrine, albumen, or 

 caseine in a state of decomposition, these 

 substances having the same composition 

 with the constituents of flesh, blood, or 

 cheese. The putrefaction of these animal 

 matters is a process identical with the meta- 

 morphosis of the vegetable matters identical 

 with them ; it is a separation or splitting up 

 into new and less complex compounds. 

 And if we consider the transformation of 

 the elements of the animal body (the waste 

 of matter in animals) as a chemical process 

 which goes on under the influence of the 

 vital force, then the putrefaction of animal 

 matters out of the body is a division into 

 simpler compounds, in which the vital 

 force takes no share. The -action in both 

 cases is the same, only the products differ. 

 The practice of medicine has furnished the 



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