324 



NATURE 



[July 31, 1879 



Gbttingen, succeeded in preparing it from material of 

 purely mineral origin. This process was to heat ammo- 

 nium cyanate, NH4.CNO, when, without decomposition, 

 a new body was formed, possessing all the properties of, 

 and undistinguishable from, urea. It has since been 

 discovered that urea is very closely connected with the 

 carbonates of anmionium, that, in fact, it is simply car- 

 bonate ef ammonium minus water. Now it appears 

 probable that urea is formed in the organism either from 

 ammonium cyanate or from ammonium carbonate, and 

 the question which Prof. Salowski, of Berlin, has tried to 

 answer is : By which process is it formed ? (vol. i. p. i). 

 As there is a general resemblance between all nitrogenous 

 food, inasmuch as it contains albumen itself, or principles 

 closely allied to albumen — among others, myosine, vitel- 

 line, serum-globuline (which form the subject of an article 

 by Th. Weyl [rol. i. p. 72]) ; and moreover, as cyanic 

 acid, carbonic acid, and ammonia, are products of decom- 

 position of albumen, the question is an open one. 



Every one knows the old plan of detecting the filcher 

 of coin from a till, by placing a secret mark on a number 

 of the coins, and so making their identity unmistakable. 

 The plan adopted by Prof. Salowski is somewhat similar, 

 though the simile is not quite applicable. There is a 

 method of putting a private mark on cyanic acid and on 

 ammonia, by using compounds containing more carbon 

 in the former case, and by employing a substituted 

 ammonia in the latter, that is, a substance possessing in 

 the main the properties of ammonia, but capable of recog- 

 nition afterwards. But as neither ammonia nor its salts 

 are normal constituents of food, it was necessary to prove 

 that by giving ammonia, a compound of nitrogen and 

 hydrogen, along with food, the amount of urea in the 

 urine is increased. Direct experiments on rabbits proved 

 the point. After feeding them on a diet of potatoes con- 

 taining a known amount of nitrogen, the amount of 

 urea eliminated was augmented by addition of salts of 

 ammonia to that diet. Now by introducing ammonia to 

 form carbonate of ammonium, two atoms of nitrogen are 

 introduced; and if that ammonia were "marked" the 

 resulting urea would be "marked" also, and would con- 

 tain two atoms of "marked" nitrogen. But, on the 

 other hand, if the reaction takes place between cyanic 

 acid (a body containing one atom of nitrogen itself) and 

 ammonia, only one atom of nitrogen would be derived 

 from the introduced ammonia, and if that ammonia 

 could be afterwards identified, the urea into which it is 

 resolved should contain only one atom of marked 

 nitrogen. 



In chemical language, let ethylamine be substituted for 

 ammonia ; in the first instance the equation should b« — 



QH,NH, + HCN0 = C0jNg^_C,H,; 

 and in the second — 



C0(C,H5. NHj)2— 2H2O = CO(NHC3H5)j. 



The former hypothesis was found to be true ; only one 

 nitrogen atom in the urea bore the mark, and the reaction 

 is proved to take place by cyanic acid and ammonia 

 combining, and then altering into urea, a body of the 

 same composition but different properties, otherwise called 

 an isonieride. 



In spite, however, of this apparently convincing experi- 

 ment, Prof. Salowski regards it as improbable that urea 

 is actually formed by the reaction between ammonia and 

 cyanic acid, unless, indeed, ammonia be suppHed directly 

 to the organism ; he takes the view that under normal 

 circumstances the urea is derived solely from cyanic acid 

 assimilating water and evolving ammonia thus : — 



2CNOH-|-HjO = CO(NHj)j-f COj. 



This would account for the increase of urea under a diet 

 containing ammonia. 



Dr. E. Baumann (vol. i. p. 60) contributes a paper an- 



nouncing the discovery of phenol, or carboHc acid, in 

 urine, and remarks that it is curious to observe a sub- 

 stance regarded as a preventive of fermentation generated, 

 although in extremely small quantity, by fermentation. 

 He also noticed the appearance of a nearly allied bod\ , 

 indicane, which, on allowing the urine to stand, change! 

 into indigo, the well-known dye. 



The colouring matter of the blood forms the subject ol 

 a series of contributions from the pen of the editor. Prof. 

 Hoppe-Seyler (vol. i. pp. 121, ii. 149). Every one ba^ 

 noticed the fact that blood from an artery has a brighter 

 red colour than that from a vein ; the cause of this is that 

 arterial blood is pumped by the heart from the lungs, 

 where it has received a supply of oxygen from the air, 

 into the arteries, which distribute it through the. body. 

 During its progress this oxygen is gradually used in 

 oxidising waste matter and in converting the spent car- 

 bonaceous substances, which have fulfilled their purpose, 

 into carbonic acid. The blood takes up this carbonic 

 acid, and in doing so its colour becomes darker. The 

 bright red principle of the blood is named oxyhaemoglo- 

 bine, and after it has turned dark it has changed to 

 hsemoglobine. Both of these substances can be sepa- 

 rated from blood by appropriate processes. When placed 

 in a tube and viewed through a spectroscope, oxyhamo- 

 globine exhibits two dark bands, Mhercas hsemoglobine 

 shows only one band, occupying a position nearly between 

 that of the two bands of oxyhsmoglobine, but slightly 

 overlapping the one at the red end of the spectrum. 

 These two substances can thus be easily distinguished 

 from each other, and as the smallest trace of oxygen con- 

 verts hsemoglobine into oxyh^moglobine, the spectrum 

 of which is easily recognised, even in presence of the 

 other, a dilute solution of the former is a very delicate 

 test for the presence of oxygen in liquids ; so delicate, 

 indeed, that one cubic millimeter of oxygen, or about as 

 much as^would occupy Jhe space of a pin-head, can be 

 detected. 



It is of course evident that, as decay, and consequently 

 removal of used-up material proceeds throughout the 

 whole body, it is impossible to obtain blood, either wholly 

 charged with oxygen or wholly free from it. Yet to be 

 able to detect oxygen in such minute quantity, it is neces- 

 sary to procure htemoglobine absolutely free from oxygen. 

 Hoppe-Seyler effects this by exposing the colouring- 

 matter of blood to a putrefying medium ; the small living 

 organisms consume the oxygen that it contains, and re- 

 duce it to hsemoglobine. He remarks, en passant, that the 

 colouring-matter of the blood withstands putrefaction 

 perfectly, as well as the action of a special ferment found 

 in the pancreas, which in this respect resembles bacteria, 

 the living organisms in ordinary putrefying media. 



This very delicate test for oxygen has been applied to 

 various animal secretions. Saliva from the parotid and 

 submaxillary glands, as might be expected from its prox- 

 imity to external air, contains oxygen, but neither gall 

 nor urine contain any, owing to the presence of easily 

 oxidised substances named bilirubine and hydrobiliru- 

 bine, by which any free oxygen is consumed. 



It is not uncommon to hear of deaths caused by sleeping 

 in an apartment in which there is a charcoal-stove. This 

 is owing to the poisonous qualities of carbonic oxide gas 

 produced by the combustion of the charcoal, and the 

 effect is not improbably due to the formation of a com- 

 pound between the hasmoglobine of the blood and the 

 gas. Blood, when charged with carbonic oxide, acquires 

 an almost vermilion-red colour. It also gives a charac- 

 teristic spectrum, and its examination shows with cer- 

 tainty the cause of death. Hoppe-Seyler has noticed 

 that, like oxyhsemoglobine, the compound of carbonic 

 oxide with hsemoglobine is not destroyed by putrefac- 

 tion, and hence blood taken from the veins long after 

 death reveals the carbonic oxide spectrum, if death has 

 resulted from charcoal-poisoning. 



