956 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



of ammonia present in the urine is increased, which indicates that an amount 

 of ammonia usually converted into urea has been taken for the neutralization 

 of the acid. 1 In a similar manner acids formed from decomposing proteid 

 may be neutralized (see pp. 950 and 993). 



The ammoniacal fermentation of the urine consists in the decomposition of urea into 

 ammonium carbonate by the micrococcus urince, the urine becoming alkaline. 



Compounds of Nitrogen with Oxygen. There are various oxides of nitrogen, the 

 higher ones being powerfully corrosive, and some of these unite with water to form acids, 

 of which nitric acid (HN0 3 ) is the strongest. Only nitrous and nitric oxides are of physi- 

 ological interest. 



Nitrous Oxide, N 2 0, likewise called "laughing-gas," is prepared by heating ammo- 

 nium nitrate, 



It supports ordinary combustion almost as well as pure oxygen, but it will not sustain life. 

 Mixed with oxygen it may be respired, producing a state of unconsciousness preceded by 

 hysterical laughter. 



Nitric Oxide, NO, is prepared by dissolving copper in nitric acid, 

 3Cu + 8HN0 3 = 3Cu(N0 3 ) 2 + 4H 2 + 2NO. 



Contact with oxygen converts it into peroxide of nitrogen (N0 2 ), which is an irritating 

 irrespirable gas of reddish color. Nitric oxide in blood first unites with the oxygen of 

 oxyhsemoglobin, forming the peroxide (N0 2 ), and then the nitric oxide combines with 

 haemoglobin, forming a highly stable compound, nitric-oxide haemoglobin (Hb-NO). 



NITROGEN IN THE BODY. Nitrogen is taken into the body combined in 

 the great group of proteid substances, which are normally completely absorbed 

 by the intestinal tract. It passes from the body in the form of simple decom- 

 position-products, in larger part through the urine, but likewise through the 

 juices which pour into the intestinal canal. The unabsorbed residues of these 

 latter juices, mixed with intestinal epithelia constitute in greater part the feces. 2 

 An almost insignificant amount of nitrogen is further lost to the body through 

 the hair, nails, and epidermis, but, generally speaking, the sum of the nitrogen 

 in the urine and feces corresponds to the proteid decomposition for the same 

 time (1 gram N = 6.25 grams proteid). When the nitrogen of the proteid eaten 

 is equal in quantity to the sum of that in the urine and feces, the body is said 

 to be in nitrogenous equilibrium. When the ingested nitrogen has been larger 

 than that given off, proteid has been added to the substance of the body ; when 

 smaller, proteid has been lost. These propositions were established by Carl 

 Voit. 



A small amount of urea and other nitrogenous substances may be excreted in profuse 

 sweating. Proteid nitrogen never leaves the body in the form of free nitrogen or of 

 ammonia. That ammonia is not given off by the lungs may be demonstrated by perform- 

 ing tracheotomy on a rabbit, and passing the expired air first through pure potassium 

 hydrate (to absorb C0 2 ) and then through Nessler's reagent. The experiment may be 

 continued for hours with negative result. 8 



1 Fr. Walther : Arehiv filr exper. Pathologic und Pharmakologie, 1877, Bd. 7, p. 164. 



2 Menichanti and Prausnitz : Zdtschrift filr Biologic, 1894, Bd. 30, p. 353. 

 8 Bachl : Zeitschrift fur Biologie, 1869, Bd. 5, p. 61. 



