156 PRACTICAL PHYSIOLOGY. [XXIV. 



B. Examination of Solid substances. 

 Physical characters. 



1. Tho. colour may suggest blood-pigment, or one of its deriva- 

 tives, or bile-pigment. 



2. Taste may indicate bile-salts, urea, or sugar. 



3. Examine microscopically to see whether amorphous or 

 crystalline. If the latter, the substance may be recognised by its 

 crystalline form, e.g., urea, uric acid, urates, leucin, tyrosin, choles- 

 terin, &c. 



4. Burn some in a tube ; smell it to detect any odour. Observe 

 if it leaves an ash. 



5. Examine its solubility in cold and warm water, caustic soda, 

 dilute acid, saline solutions, alcohol and ether. Test the solution 

 in the first four reagents as directed under examination of fluids. 

 Examine the ethereal solution iov fats and cholesterin. 



Cholesterin.: — (i.) Evaporate a little of the ethereal solution in 

 a watch-glass, and add a drop of strong H^SO^. A red colour 

 indicates cholesterin. (2.) Examine microscopically. Cholesterin 

 crystallises from ethereal solution in colourless needles, from solu- 

 tion in boiling alcohol in its characteristic plates. 



C. Analysis of Urine. — The student must also practise the 

 analysis of urines containing one or more abnormal constituents, 

 and he must also practise the estimation of the quantity of the 

 more important substances present. Both sets of processes must be 

 done over and over again, in order that he may perfect himself in 

 the methods in common use. 



