Urea

“ Lastly, to these must be added those closely related substances, the purin bodies, the end-products of nuclein as opposed to general protein metabolism, of which latter urea is the terminal product. To sum up, in a man on ordinary diet about 90 per cent. of his total nitrogen is excreted as urea, about 3 per cent. as ammonia, the residue of the nitrogen appearing in the form of other nitrogenous metabolites.
Seat of Formation of Urea
The liver, it is generally held, is the main centre wherein urea is produced from the amino-acids ”

“ When we reflect that some hundreds of thousands of tons of urea are daily deposited, which ordinary plants are unable to assimilate until considerable changes have been undergone, the question is of importance, What happens Nitrogen bacteria.in the meantime? In effect the urea first becomes carbonate of ammonia by a simple hydrolysis brought about by bacteria, more and more definitely known since Pasteur, van Tieghem and Cohn first described them. ”

“ Urea (CON2H4) the principal waste product of nitrogenous matter, is always present in considerable amount. The sound horse may eliminate 100 to 200 grammes daily, the dog 5 to 180 grammes. It is present in excess in all fevers and inflammations unless urination is suspended or impaired, in cryptogamic diuresis, in mellituria, uræmia, nephritis and cystitis. Test: The addition to a filtered solution of urine, freed from phosphates, of solution of acid nitrate of mercury, precipitates it as nitrate of urea. ”

“ The amount of urea excreted is to be regarded, to a certain extent, as a measure of the physiological wear of the muscular system, which wear is increased by muscular exertion, there being a corresponding increase in the excretion of urea by the kidneys. This wear of the muscular system is being constantly repaired by the nitrogenized elements of food. In discussing, then, this question, physiologists have come to speak of the excretion of nitrogen as measuring, more or less accurately, the physiological wear of the muscular system. ”

“ Nitrogen that has served its purpose as muscle or other proteid leaves the animal economy chiefly in the form of urea, and its proportion in the urine, therefore, is a fair index of the activity of wasting influences. ”

“ Urea is undoubtedly a product of the oxidation of complex nitrogenous matters (albumin) of the animal body. It is found in the blood. It is absorbed from the blood by the kidneys. A man excretes about 30 grams of urea per day. As a derivative of carbonic anhydride, into which it is readily converted, urea is in a sense a product of oxidation.
[39 bis] Its polymer, C3N3H3O3, is formed together with it. Cyanic acid is a very unstable, easily changeable liquid, while cyanuric acid is a crystalline solid which is very stable at the ordinary temperature. ”

“ This urea is carried by the blood stream from the liver to the kidneys where it is passed out to become the chief organic substance in urine. The more protein one eats the more surplus amino acids will there be, and so the more urea will be formed and passed out of the body. Flesh-eating animals and men (Eskimos for an example of the latter) eat a very large surplus of proteins, the fuel for their metabolism being furnished almost altogether either from the usable remains of the decomposed amino acids or the fats that were in the flesh they ate. ”

“ UREA, or Carbamide, CO (NH2) 2, the amide of carbonic acid, discovered in 1773 by H. M. v. Rouelle, is found in the urine of mammalia, birds and some reptiles; human urine contains approximately 2-3%, a grown man producing about 30 grammes daily. It is also a constituent of the blood, of milk, and other animal fluids. ”

“ But urea, in comparison with most animal or vegetable products, is of simple structure. It contains but one atom of carbon in each molecule, whereas many others contain a very large number of carbon-atoms. The transformation of cyanate of ammonia into urea, which took place so readily, was a very simple one, if we consider merely the relation of the two bodies to each other. They have exactly the same composition. They contain the same percentages of carbon, hydrogen, nitrogen, and oxygen. ”

“ They differ also in regard to their saline ingredients; and while salts of potash and soda form the principal part of the ash of the urine of the ox, sheep, goat, and horse, and phosphoric acid and phosphates are entirely absent, that of the pig contains a considerable quantity of the latter substances, and in this respect more nearly resembles the urine of man. Human urine is also much richer in urea and nitrogenous constituents generally, and has a higher value than any of the others. ”

“ It was shown that a close match could be obtained with these components of the closed environment.
Less abundant, though no less important, are the nonwater components of urine and feces. The urine is important for the content of fixed nitrogen and other products of man's metabolism and serves as a very effective substrate for cultivation of hydrogen bacteria. Maximum closure of the system necessitates utilization of the urea in urine as a nitrogen source.
The average man produces 1.2 to 1.6 liters of urine per 24-hour period. ”

“ In this state the urea, ammonia, and other products of digestive or putrefactive decomposition are partially oxidized and in this oxidation the available oxygen present is rapidly consumed, the conditions in the sewage becoming anaërobic. The second state is putrefaction in which the action is under anaërobic conditions. The proteins are broken down to form urea, ammonia, the foul-smelling mercaptans, hydrogen sulphide, etc., and fatty and aromatic acids. The carbohydrates are broken down into their original fatty acid, water, carbon dioxide, hydrogen, methane, and other substances. ”

“ A crystalline precipitate of nitrate of urea may give rise to error if the urine be very concentrated or the experiment conducted in the cold. This may be distinguished by its disappearance on warming or by the microscope. The action of the nitric acid on the coloring matter of the urine, forming a dark band at the point of junction, may obscure the reaction, but with care will not give rise to mistakes. ”

“ Furthermore, Levy’s hypothesis involves the assumption that the excreting functions of the kidney for uric acid and urea are separate and independent of each other, and to discussion of this we now pass on.
The Relationship, if any, between the Amounts of Uric Acid and of Urea, and Total Non-Protein Nitrogen in Human Blood
Taking samples of human blood from (1) unselected insane subjects and (2) chronic nephritics, Folin and Denis determined the amounts therein of urea, total non-protein nitrogen, and uric acid. ”

“ The glands apparently are acted on more strongly by a solution of urea, and less strongly by an infusion of raw meat, than are the processes. The case of urea is particularly interesting, because we have seen that it produces no effect on Drosera, the leaves of which are adapted to digest fresh animal matter. But the most important fact of all is, that in the present and following species the quadrifid and bifid processes of bladders containing decayed animals generally include little masses of spontaneously moving protoplasm; whilst such masses are never seen in perfectly clean bladders. ”

“ When the urea is stationary, which is most frequently the case, it is necessary to calculate the coefficient of oxidation; that is, the relation existing between the solid matters of the urine and the urea. The elevation of the coefficient is prima facie evidence the obesity is due to excess of assimilation, while depression of the coefficient indicates default of assimilation. ”

“ Also, Flack and Hill, discussing the metabolism of nuclein, hold that some of the uric acid thus formed may be transmuted into urea by an uricolytic ferment present in the liver, muscles, and kidneys. This same agent they consider “probably destroys a considerable amount of the uric acid formed in the body. Indeed, uric acid, even when given in the food, owing to the presence of this enzyme, causes no increase in the uric acid output of the body.” ”

“ It is always advisable to mention the reaction to test papers of all samples received. Urine is normally acid, but there are certain diseases which render fluid neutral or alkaline. The urea of acid urine on standing is changed by a putrefactive ferment into ammonic carbonate, but this decomposition in a state of health should not take place for at least twenty-four hours. ”

“ We must therefore assume that in the blood or in other parts of the body, wherever nitrogenous compounds are oxidized, carbonic acid is constantly formed. From this salt the formation of urea must take place by the elimination of water, a reaction which has long ago been effected by heating the salt to 140° with absolute alcohol. In the organism this elimination of water must evidently take place in a different manner, and especially at the temperature of the body. ”

“ URIC ACID, C5H4N4O3, in organic chemistry, an acid which is one of the penultimate products of the tissue waste in the human body. While the bulk of the nitrogen of the albuminoids passes off through the bladder as urea, a small portion of it stops at the uric acid stage. Human urine contains only a fraction of a per cent. ”

“ The composition of the urine and the quantity excreted vary considerably, being influenced by the moisture and temperature of the atmosphere, by the character of the food consumed, and by the empty or replete condition of the alimentary tract. On an average a healthy man secretes about fifty ounces of urine in the twenty-four hours. This quantity usually holds in solution about one ounce of urea, and ten or twelve grains of uric acid. In the amount of other animal matters, and saline substances, there is great variation, the quantity of these ranging from a quarter of an ounce to an ounce. ”

“ It has been calculated that the average amount of urea daily formed in the body of a healthy man is about 470 grains. To supply this daily consumption of nitrogenous matter, it is necessary that about four ounces of flesh-forming substance should be consumed daily. It is important, therefore, to inquire how this substance may be obtained. ”

“ The urine is a yellowish fluid which varies greatly in its depth of colour, from pale amber to a deep brown. It has a specific gravity of about-1020, varying with the percentage of solids in solution, and it usually has an acid reaction. It is a fluid of complex character, containing, as already mentioned, practically all the waste nitrogen of the body. Among the principal organic substances present are urea, ammonia, purins (uric acid and the so-called purin bases, xanthin, &c.) ”

“ On the other hand, numbers of leading physicians, including especially those highly educated gentlemen who cultivate a consulting practice, are in the habit of pushing urinary analysis almost to an excess. One well-known specialist of the writer's acquaintance, with an extensive West End practice, makes quantitative determinations of urea, uric acid, and total acidity, in addition to conducting other diagnostic experiments, on every occasion that he interviews his patients. ”

“ The nitrogenous components become oxidised, and urea ultimately formed, which being very soluble is freely excreted by the sudorific glands p. 23in the perspiration, and by the kidneys in the urine. The non-nitrogenous compounds are also changed by the action of oxygen into carbonic acid, which is expelled from the system by the lungs. If the natural functions are not perfectly and with regularity performed, the balance of power must of necessity be lost, and disease engendered. ”

“ They improve and purify the diseased state of the blood and lymph, principally when it shows itself by an accumulation of albuminous azotic compounds, and by a tendency to form urea, uric acid and stone in the bladder. ”

“ The nitrogenous Aliments are needed particularly to supply the growth and waste of the muscular and nervous tissues, which both contain Nitrogen; as also do all the parts of the body, excepting Fat. This waste is continually going on. It depends upon the fact that, after having lasted a certain time, the particles of all these tissues are gradually displaced, oxidized, and conveyed away out of the blood into the urine and other secretions. In the urine these waste matters are found as Urea, Uric acid, and Kreatine. ”

“ F. then related a remarkable case of acute inflammation of the kidneys in which the patient exhibited the characteristic symptoms of poisoning from the retention of urea. After other remedies were tried in vain, the patient’s life was 68saved by the simple administration of water as a beverage at short intervals. The diuretic effects of the water soon washed away the poison and gave immediate relief. ”

“ The changes of the gases in the blood, together with the processes which take place in the intestines or in the liver, and which have so often been made the subject of the most thorough investigations, would be beyond the reach of our methods and we could only determine that these organisms have the power to convert comparatively large quantities of albumen into carbonic acid, water, and urea, with the absorption of oxygen—in short, the process would be similar to that of yeast fermentation. ”

“ The urine was dark and slimy, reddish, slightly acid, and had at the bottom of the bottle brick-dust settlings. Heat did not show albumen, but by heating it the dark urine became clearer, and contained also salts of uric acid. I ex [Pg 336] amined the kidneys of the patient, found them sensitive against pressure, and the diagnosis pointed to chronic catarrh of the kidneys. Sleeplessness, pain in the back and the tired feeling in the upper parts of the thigh were additional symptoms of this malady, and I determined to use Virga-aurea. ”