106 CHEMICAL PHYSIOLOGY. 



9. Preparation of Creatinin. Take 250 cc. of urine, precipitate 

 it with milk of lime, and filter. Evaporate the nitrate to a 

 syrupy consistence, and extract it with alcohol. Filter, and to 

 the filtrate add a drop or two of a neutral solution of zinc chlo- 

 ride, and set the vessel aside. After a time creatinin-zinc-chlo- 

 ride is deposited on the sides of the vessel. 



10. Tests and Reactions. 



(a.) Examine the deposit microscopically. It forms round 

 brownish balls, with radiating lines (Fig. 29). 



(b.) Weyl's Test. To urine add a very dilute solution of 

 sodic nitro-prusside, and very cautiously caustic soda = a 

 ruby-red colour, which is evanescent, passing into a straw 

 colour. 



11. Colouring- Matters of the Urine. 



Several colouring-matters seem to be present in the urine, 

 including : 



(1.) Urobilin, which occurs especially in the high-coloured urines-' 

 of fever. It gives urine its red or reddish-yellow colour, and 

 on the addition of ammonia it becomes yellow. 



(2.) Uro- Chrome is a yellow pigment. When a watery solution 

 is exposed to the air it oxidises, and becomes red owing to the 

 formation of uro-erythrin. 



(3.) Indigo-forming Substance (Indican). This is derived from 

 indol, C 8 H 7 N, which is developed in the intestinal canal from the 

 pancreatic digestion of proteids, and also from the putrefaction of 

 albuminous bodies. It may also be formed from bilirubin. In 

 urine it is a yellow pigment, and is more plentiful in the urine 

 of the dog and horse. 



12. General Reactions. 



(a.) Add to normal urine a quarter of its volume of HOI, 

 and boil = a fine pink or yellow colour. 



(b.) Add nitric acid = a yellowish-red colour, usually 

 deeper than the original colour. 



(c.) To two volumes of sulphuric acid in a test-tube, add 



