Vol. XXII. No. 7.] 



POPULAR SCIENCE 1<5"EWS. 



109 



ifleliictne anH JP^armatp. 



UREA. 



An important product of the decomposi- 

 tion of the nitrogenous tissues and foods of 

 the bod}' is a substance linowu as urea, which 

 is excreted in large quantities through the 

 urine. It is a highly crystalline bodj', ver}- 

 soluble in water, and containing 46| per cent 

 of nitrogen. More than nine-tenths of all the 

 nitrogen taken into the system is excreted in 

 this form. It is supposed that the liver is the 

 chief organ concerned in its formation. An 

 adult excretes about five hundred grains of 

 urea daih', although the amount varies consid- 

 erabl}- under different circumstances. 



In certain diseases and conditions of the 

 s^-stem, urea is formed in abnormall}' large 

 quantit}-. The exact quantitative determina- 

 tion of the amount present is a matter of some 

 difficulty, but an approximate test is easily 

 made by adding to a sample of the urine an 

 equal amount of pure, strong nitric acid. This 

 should be done in a test-tube which is kept 

 cool by being placed in a vessel of cold water. 

 If an excessive amount of urea is present, 

 beautiful groups of tabular crystals of nitrate 

 of urea will separate out in the course of ten 

 or twenty minutes. These crj-stals will not 

 develop in normal urine unless it has been 

 ivreviously concentrated by evaporation. 



From a chemical point of view urea is a sub- 

 stance of the greatest interest and irajiortance. 

 Its chemical name is carbamide, and it has the 

 symbol CO (NHj)^. It is best considered as 

 a substituted ammonia formed from two mole- 

 cules of ammonia (NHg)^ by replacing two 

 atoms of hydrogen, one from each molecule of 

 ammonia, by the dyad radical CO. The great- 

 est point of interest about it, however, is, that 

 it is the first organic substance ever made arti- 

 ficially from inorganic materials. It was for- 

 merly' a favorite theory' among chemists that 

 the line between inorganic and organic bodies 

 was impassable, and that the latter could only 

 be formed through the agency of a living 

 organism, either vegetable or animal. In 1828, 

 however, the German chemist Wohler discov- 

 ered that by heating a solution of iso-cyanate 

 of ammonia, a strictlj' inorganic salt, it was 

 transformed into urea, which had hitherto been 

 known onl}' as a product of the animal organ- 

 ism. The iso-C3'anate of ammonia is isomeric 

 with urea ; that is, it contains the same ele- 

 ments in the same proportions : so the great 

 difference in the phj'sical properties of the two 

 bodies must be due to the different arrange- 

 ment of the atoms which compose the molecule. 

 A comparison of the so-called graphic symbols 

 of the two substances will make this distinc- 

 tion clearer. 



Iso-cyanate of ammonia. Urea. 



= C = N — N = H,, = C = ^ "^^-^ 



N = Hj 



The actual symbol (CON^HJ is the same in 

 both cases, but the grouping of the elements 

 is entirel}' different. It should also be ob- 

 served, that, in tiie transformation to urea, one 

 of the nitrogen atoms changes its quantiva- 



leuce from three to five (see May number, p. 

 73). In later years a very large number of 

 organic bodies have been made artificiallj'. 



Urea forms an immense number of com- 

 pounds and derivatives which are only of inter- 

 est to the chemist. The most important one 

 physiologicall}- is uric acid (C^lI^N^Og) , which 

 is present in small quantity- in human urine, 

 but is the chief ingredient of that of birds, 

 reptiles, and insects. The excrement of birds 

 contains a very large percentage of this acid 

 in combination with ammonia, and the great 

 value of this material as a fertilizer is due to 

 the large percentage of nitrogen a\ailable for 

 plant-food which it contains. 



Hippuric acid (CgHgNOg) occurs in large 

 quantity' in the urine of horses and other her- 

 bivorous animals, but that of man and the car- 

 nivora only contains a trace. 



Although urea is itself a product of decom- 

 position, it is not verj' stable, and tends to 

 break up still further into salts of ammonia, 

 the odor of which is very perceptible in decom- 

 posing urine. It is interesting to trace in the 

 imagination the transformations which an atom 

 of nitrogen ma^- undergo. As a constituent 

 of ammonia it may be absorbed by the grow- 

 ing plant, and take its place in the compli- 

 cated structure of some nutritive vegetable 

 material ; thence it passes into the body of a 

 sheep or ox, and becomes a part of its gelatin 

 or albumen. Then it may be appropriated by 

 a member of the human faraih', giving strength 

 to his muscles and vigor to his constitution. 

 But having thus performed its part, it is 

 changed by the mysterious vital processes into 

 urea, which, breaking up into a still simpler 

 substance, sets the nitrogen free in the form of 

 ammonia, read}' to be appropriated by another 

 plant, and again pass through tlie same circle. 

 These changes are no matter of fanciful specu- 

 lation, but arc actually' occurring every day, 

 and arc a striking proof of the scientific axiom, 

 that matter may change its form continually, 

 but can never be destroyed. 



THE RIND OF FRUIT INDIGESTIBLE. 

 That the rind, or " skin," of all fruit is more 

 or less indigestible, is a fact that should not be 

 forgotten. We say all fruit, and the state- 

 ment must be understood to include the pelli- 

 cle of kernels and nuts of all kinds. The 

 edible part of fruit is peculiarly delicate, and 

 liable to rapid decomposition if exposed to 

 the atmosphere ; it is, therefore, a wise pro- 

 vision of nature to place a strong and imper- 

 vious coating over it, as a protection against 

 accident, and to prevent insect enemies from 

 destroying the seed within. The skin of plums 

 is wonderfully strong compared with its thick- 

 ness, and resists the action of water and many 

 solvents in a remarkable manner. If not 

 thoroughly masticated before taken into the 

 stomach, this skin is rarely, if ever, dissolved 

 by the gastric juice. In some cases pieces of 

 it adhere to the coats of the stomach as wet 

 paper clings to bodies, causing more or less 

 disturbance or inconvenience. llaisins and 

 dried currants are particularl}- troublesome in 



this wa}-, and, if not chopped up before cook- 

 ing, should be thoroughly chewed before swal- 

 lowing. If a dried currant passes into the 

 stomach whole, it is never digested at all. 



In the feeding of domestic animals this fact 

 should be kept in mind. If grain and legumi- 

 nous seeds are not crushed or ground, much of 

 the food is often swallowed whole, and the 

 husk or pellicle resists the solvents of the 

 stomach, causing a considerable loss of nutri- 

 ment. Birds, being destitute of teeth, are 

 provided with a special apparatus for grinding 

 their seed ; namely, the gizzard. 



The indigestibility of certain nuts is par- 

 tially due to the brown skins. Blanched 

 almonds on this account are more digestible 

 than those which have not been so treated. 



[Original in Popular Science Neu>a.\ 



SOME FACTS CONCERNING BRIGHT'S 

 DISEASE. 



BY JOHN CROWELL, M D. 

 II. 



The chronic form of Bright's disease presents 

 three types, which may be summed up as, first, the 

 smooth, white kidney; second, the granular, mottled 

 kidney; third, the waxy or amyloid kidney. In 

 the first form the structural change extends to the 

 fibrous substance, in which the fatty degeneration 

 is found, causing enlargement of the organs to 

 double their natural size, and giving them a yellow- 

 ish-white appearance. Hence the name, smooth, 

 white kidney. In the granular form the kidneys 

 are diminished in size and weight, and the texture 

 is tough and unyielding. The urine is at first 

 copious and of less specific gravity. As the dis- 

 ease advances, the quantity diminishes, the albu- 

 minous deposit is slight, and occasionally absent. 



In the majority of cases tlie urine contains 

 epithelium and granular casts, which are eliminated 

 from the uniferous tubes. Out of two hundred 

 and fifty cases of this form of the disease exam- 

 ined by Dickson, the average age of the patients 

 was about fifty years. In the waxy form the 

 kidney is usually enlarged. The true nature and 

 source of this waxy material has never been defi- 

 nitely determined. Dickson supposed it to be a 

 species of fi brine containing less alkali and a 

 larger proportion of earthy salts. Virchow be- 

 lieved that -it belonged to the same class of sub- 

 stances as salt and cellulose tissue, on account of 

 its yielding a violet color when combined with 

 sulphuric acid and iodine. 



The albumen at first is slight, becoming quite 

 profuse as the disease advances. The urine is pale, 

 containing epithelium cells and fat corpuscles. 



An interesting condition of the urine in this dis- 

 ease is noted by De Beauvais, who states that the 

 odor imparted to healthy urine by the digestion 

 of asparagus is wanting, and that the smell of 

 violets, so familiar, which the renal secretion gives 

 off in patients taking turpentine, as well as the 

 smell of pepper from the taking of cubebs, are 

 generally absent. 



The immediate cause of death is variable. 

 About one-third of the victims of the chronic form 

 perish by uraemie poisoning, either in the form of 

 coma and convulsions, or irrepressible diarrhoea and 

 vomiting. Some die from the dangerous situation 

 of the dropsical effusion, as when the glottis or 

 the lungs are invaded. About one-fifth die of 

 secondary pneumonia, pericarditis, or double 

 pleurisy. 



The great danger in this disease lies in the 

 enervation of the organic nervous system. It i,s 



