182 INTRODUCTION TO GENERAL PHYSIOLOGY 



which must be capable of rotation. In the absence of the solution, 

 adjust the position of the second prism so that the field is as dark 

 as possible. Interpose the solution. If optically active, the field 

 will become light. In the case of cane-sugar, the second prism 

 (analyser) must be rotated in the direction of the movement of the 

 hands of the clock in order to restore darkness ; in that of egg- 

 albumin, in the opposite direction. The actual amount of rotation 

 must not exceed 180 in this experiment, otherwise confusion may 

 result. If in doubt, dilute the solution until the fact of rotation can 

 be only just made out. 



A more accurate and sensitive polarimeter is necessary for 

 certain important experiments with enzymes to be described later. 



Waste Products 



To prove the production of carbon dioxide in the course of 

 vital reactions, all that is needed is to breath out through a tube 



FIG. 12. Urea Apparatus. 



A, large test-tube, immersed in warm water. 



B, bottle containing acid, connected to a filter pump. 



into recently filtered lime water, or solution of barium hydroxide. 

 The precipitate is shown to be carbonate by its solution in dilute 

 acetic acid. 



The chief waste-product of nitrogen metabolism is urea, which 

 is excreted in the urine. To prove its presence, the best method is 

 to convert it into ammonium carbonate by the agency of the enzyme 

 urease, found in Soy beans and elsewhere. A lew beans are ground 

 in a coffee mill, the powder sifted through a sieve, and a portion of 

 what passes through is added to some fresh urine in a closed bottle. 

 Allow to stand for an hour or two in a warm place. On opening 



