HI 



CHEMISTRY. 



[THB BBCRrnojre. 



In its coono from the heart through the tissues, the 

 YNtoo* blood is therefore formed, which in the great 

 circulation flows back again to the heart ; and this 

 blood, which in nourishing the tissues has undergone 

 such important changes, is supplied again with oxygen 

 while passing through the lungs, and thus adapted, in 

 return, for the nutrition of the tissues; in short, it is 

 transformed again into arterial blood. 



As the ovum represents, among the secretions, a 

 transition stage between these and the tissues, the lungs 

 may be considered as organs, holding, in respect of their 

 functions, an intermediate position between reception 

 and separation. Carbonic acid and water are the excre- 

 tions which they give out, and in return they take in 

 oxygen. Without oxygon, no arterial blood, and with- 

 out arterial blood, no nutrition could bo produced. 1 i 

 the nutrition be interrupted, tlio functions of all tissues 

 are deranged. The muscles cannot contract themselves, 

 the nerves lose their irritability, the reasoning faculty 

 of the brain is disturbed, if the blood cease to furnish 

 these organs with their peculiar combinations ; and this 

 Utter process is dependent on the supply of oxygen ; for 

 all organic constituents of the blood are gradually trans- 

 formed by oxygen. The albuminous and fatty sub- 

 stances have, without any exception, so great an affinity 

 for oxygen, that they are gradually decomposed into 

 combinations containing it. Oxygen passes also through 

 the capillaries into the tissues themselves ; therefore the 

 venous blood contains less oxygen than the arterial, and 

 the manifold decomposition becomes possible to which we 

 hare already stated the tissues are subjected. 



We recognise in the flesh-principle, the flesh-basis, and 

 the flesh-acid, a few of the intermediate stages through 

 which the albuminous substances pass by the influence of 

 oxygen. The last results of this influence are the urine- 

 principle, or urea, carbonic acid, and water. The dif- 

 ferent fats are also transmuted into carbonic acid and 

 water, with even greater readiness than albumen, as their 

 greater amount of carbon and hydrogen facilitates their 

 combustion with oxygen. Tims, we daily exhale through 

 the lungs, in form of carbonic acid and water, about one- 

 third part in weight of the nutriment we have token. 

 As this combustion depends upon nothing else than a 

 combination of oxygen with other elements, it follows 

 clearly, that the inhaled oxygen, the affinity of which 

 acts slowly but without interruption, burns down entirely 

 all the organic substances of the blood.* For tliis pro- 

 cess four or five days only are requisite. 



This act of combustion, in great part, explains why the 

 temperature of the human body continually exceeds that 

 of the surrounding atmosphere. The difference between 

 the temperature of the latter and of our own body is, in 

 scientific language, designated as proper heat. This 

 proper heat varies according to the temperature of the 

 external air, while the actual heat always remains the 

 same. The average amount of the latter is 98 F. , with- 

 out fluctuating a single degree during health. 



27. Though a part of the albuminous matters of the 

 blood is lost from the body with the exhaled air, in the 

 form of carbonic acid and water, still the kidneys are the 

 principal organs which withdraw the waste albuminous 

 bodies from the blood ; for the urine, which is excreted 

 by the kidneys, collected in the bladder, and voided ex- 

 ternally by the urethra, is a solution in which urea, uric 

 acid, nosh-basis, and flesh-principle are contained ; all 

 Injinjt substances whoso amount of nitrogen, carbon, 

 hydrogen, and oxygen, evinces their origin from the 

 albuminous substances. 



The flesh-basis and flesh-principle we have already de- 

 scribed. They are present in the urine, but in very 

 small quantities. This excretion contains also, in a 

 somewhat greater quantity, uric acid a substance 

 scantily soluble in cold water, which, however, is dis- 

 solved in the urine as a urate of soda. Urea is easily 

 soluble in water, aud is contained in the urine in the 

 most abundant quantity. 



B Slides the uric acid, the human urine sometimes also 



SOT !,, p. si). 



t It hat tow Ulcly dlM-omd, that an MM of flbrine, when taken u 



contains some lactic and butyric acids, with another acid 

 nitrogenised, and peculiar to the urine of herbivorous 

 animals, which chemists call uric acid of horses, or 

 hipptiric acid, as having been first detected in the urine 

 of those animals. 



lint none of these acids have been found in the urine 

 in an unoombined state. The acid reaction, however, of 

 this excretion, is produced by an inorganic salt, termed 

 acid phosphate of soda, in which the acid predominates. 

 The more important concomitants of this salt in the virine, 

 are common salt and alkaline sulphates ; but chloride of 

 potassium, aud the phosphates of lime and magnesia, are 

 also found in the urine, which sometimes also contains 

 traces of iron and of fluoride of calcium. 



The quantity of urine voided in twenty-four hours, 

 amounts to about one-third of the weight of the nutri- 

 ment taken in the same time. 



28. Constituenti of the Secretions. It is a very general 

 popular belief, that the excrements are only formed from 

 the undissolved remains of food. Though these consti- 

 tute a not inconsiderable portion, it is quite a mistake to 

 suppose that this excretion is not essentially mixed with 

 other constituents, owing their origin to the blood ; for 

 how could wo doubt that the capillaries, which exist in 

 the intestinal walls in such abundance, would allow any 

 substances to transude into the intestinal cavity, as this 

 iransudation is the indispensable condition of any transi- 

 tion of dissolved substances into these blood-vessels 1 

 All animal membranes, which are moistened on each side 

 by different fluids, permit substances to pass through in 

 such a manner, that the matters transuding from one side 

 arc replaced by those which similarly pass from the other. 

 The excrements are also mixed with a proportion of 

 digestive fluids, mucus, products of decomposition from 

 the bile, horny cellules from the mucous coating of tlio 

 intestines, and other substances, which, when onco 

 secreted, do not return again to the blood. 



The undissolved remains of our nutriment, which form 

 the excrements with the substances just mentioned, are 

 in part the insoluble, or hardly soluble constituents of 

 the food, as the clastic fibres of animal food, and the 

 cellular principles of vegetable nutriments, of which we 

 shall treat in detail hereafter. There will also be found 

 in the excrements such aliments as of themselves .-in- 

 soluble in the digestive fluids, if the quantity of the 1 

 have been too small in proportion to the nutriment to r 

 its solution. Thus, a very great variety exists in the com- 

 position of the organic constituents of the excrements. 



Of the inorganic constituents of our food, the rectum 

 discharges, more especially the earths, the lime and 

 magnesia salts, together with a considerable quantity of 

 iron, on which, as well as on the constituents of the bile, 

 the colour of the excretions is principally dependent. 

 The soluble salts of the alkalies are also to be foun 

 these excretions, partly transuded from the capillaries of 

 the intestines, t 



29. Excreting Powers of the Skin. Besides the lun^s, 

 the kidneys, and the rectum, the skin has to be nn-u- 

 tioned as another most important organ of excretion. 

 Not only do the capillaries of the skin keep up an unin- 

 terrupted discharge of carbonic acid, and take in oxygen 

 in return ; but this organ is also abundantly provided 

 with small glands of two kind, excreting from the Mood 

 the perspiration and the sebaceous or greasy subsi 

 of the skin, which are therefore called sudoriferous and 

 seliiperous glands. 



The perspiration contains many regularly detached 

 scales of the epidermis. Besides a small quantity of fat, 

 several volatile organic acids, consisting only of carbon, 

 hydrogen, and oxygen, are the principal constituents of 

 the perspiration. The chemist calls these butyric, butyro 

 acetic, and formic acids, and classes them in one group 

 as being in their composition very similar to the fatty acids, 

 to wlu'ch butyric acid belongs ; also with respect to t 

 various properties. These acids occasion the sourness 

 of tlio perspired fluid. Common salt, chloride of potas- 

 sium, sulphates and phosphates of the alkalies, and traces 



food, U atwayi excreted from Uw boclT, br the rectum, la an unchanged 

 uu. Ei>. 



