154 PRACTICAL PHYSIOLOGY. [XXIV. 



APPENDIX. 



Exercises on the Foregoing. 



A. The student must practise the analysis of fluids containing 

 one or more of tlie substances referred to in tlie foregoing 

 Lessons. 



No hard and fast rule can be laid down for the examination of 

 the fluids met with in physiological work at all comparable with the 

 method employed in inorganic chemistry. To begin with, the 

 student must be largely guided by the physical characters, — colour, 

 smell, taste, etc. — of the fluid he is dealing with, and these will 

 usually give him a satisfactory clue as to the chemical tests he 

 should employ. 



N.B. — In all cases concentrate some of the fluid for subsequent 

 use if required, and complete the concentration on a water-bath to 

 avoid overheating or charring. 



A colourless solution should be examined for proteids and carbo- 

 hydrates by the method described in Lesson lY., p. 32. Marked 

 opalescence will indicate milk or glycogen, less distinct opalescence 

 may suggest the presence of starch or certain proteids. Colourless 

 solutions may also contain urea, bile-salts, leucin, tyrosin or fer- 

 ments. 



Colour: — A red colour will suggest blood, a green tint bile, a 

 yelloio urine, a brown methcemoglobin or haematin. If blood- 

 pigment or one of its derivatives is suspected, use the spectroscope 

 at once, and observe the spectrum of (a) the original solution, (b) 

 the same shaken with air, and (c) after the addition of (NH^)2S. 



The smell may give an indication as to the presence of bile or 

 urine. Do chemical tests accordingly. 



Taste : — If salt, examine for globulins or urea, if bitter for bile- 

 salts, if siveef for sugars. 



Following the indications obtained from the physical characters, 

 select from the following chemical tests those applicable to the 

 fluid which is being examined. 



1. Test for proteids by xanthoproteic and Millon's tests, and for 

 carbohydrates by iodine and Trommer's test. The tests for special 

 proteids and carbohydrates have been already described (p. 32). 



2. Blood : — Test chemically for proteid constituents. 



3. Bile: — Do Gmelin's test for bile-pigments, and, if proteids 

 are absent, Pettenkofer's test for bile-acids. If proteids (not pro- 

 teoses and peptones) are present, neutrahse, boil, filter, and test 

 filtrate for bile-salts. Remove proteoses and peptones, if present, 

 by precipitation with alcohol, filter and test filtrate for bile-salts. 



