120 PRACTICAL PHYSIOLOGY fxiX. 



increased in the food, and is diminished by vegetable diet. It is increased 

 by copious draughts of water, salts. It is still excreted during starvation. 



(b.) Muscular Exercise has little effect on the amount. 



(c 1 .) In Disease. In the acute stage of fevers and inflammation there is an 

 increased formation and discharge, also in saccharine diabetes (from the large 

 quantities of food consumed). It is diminished in anaemia, cholera, by the 

 use of morphia, in acute and chronic Bright's disease. If it is retained within 

 the body, it gives rise to ur*mia, when it may be excreted by the skin, or be 

 given oil by the bowel. 



10. Occurrence. Urea occurs in the blood, lymph, chyle, liver, lymph 

 glands, spleen, lungs, brain, saliva, amniotic fluid. The chief seat of it.s 

 formation is very probably the liver. It also occurs in small quantity in 

 the urine of birds, reptiles, and herbivora. but it is most abundant in that 

 of carnivora. 



LESSON XIX. 

 VOLUMETRIC ANALYSIS FOB UREA. 



1. Before performing the volumetric analysis for urea, do the 

 following reactions, which form the basis of this process : 



(n.) To a solution of sodic carbonate add mercuric nitrate = a 

 yellow precipitate of mercuric hydrate. 



(//.) To urine add sodic carbonate, and then mercuric nitrate = 

 first of all a white cheesy precipitate ; on adding more mercuric 

 nitrate, a yellow is obtained, i.e., no yellow is obtained until the 

 mercuric nitrate has combined with the urea, and there is an excess 

 of the mercuric salt. 



(c.} To urine add hypobromite of soda. At once the urea is 

 decomposed, and bubbles of gas N are given off. 



2. Estimation of Urea by Hiifner's Hypobromite Method. 



The principle of this method depends on the fact that urea is 

 decomposed by alkaline solution o"f sodium hypobromite, yielding 

 water, C0 2 and N. The C0 2 is absorbed by the caustic soda, the 

 ]N", which is disengaged in bubbles, is collected and measured in a 

 suitable apparatus. 



Sodium Carbon Sodium 



Urea. Hypobromite. Dioxide. Nitrogen. Water. Bromide. 



= C0 2 + N 2 4- 2H 2 



Every o.i gram of urea contains .046 gram "N this at the ordi- 

 nary temperature and pressure = 37.3 cc. of nitrogen. In practice- 

 only 35.43 cc. are obtained. It is an accurate method, and the 

 one generally used for clinical purposes. Many different forms of 

 apparatus have been devised, including those of Knop and Hiifner, 

 Eussel and West, Graham Steele, Simpson, Dupre, Charteris, 

 Gerrard, &c. 



