454 PEACTICAL PHYSIOLOGY 



BACTERIAL DIGESTION. 



This is studied by allowing the artificial pancreatic digest to proceed 

 icithout the addition of thymol. To obtain the aromatic bodies (see 

 p. 227) which are produced, the following method is employed : 



The digest is placed in a large flask connected with a Liebig's 

 condenser and distilled, the distillate being received in a smaller flask. 

 After distilling for about an hour, a sample is removed from the distil- 

 late, to which the following reactions for aromatic bodies may be 

 applied : 



(1) Note the penetrating faecal odour. 



(2) Legal's Test. Place about 5 c.c. of the distillate in a test-tube 

 and add a drop or two of a weak watery solution of sodium nitro- 

 prusside. A red colour results, which is very much intensified by 

 the addition of a drop of 20 per cent, caustic potash. Now acidify 

 with acetic acid, when the red colour will be replaced by blue. 

 These are the colours obtained when indol is in excess ; if skatol be 

 in excess the red is replaced by a yellow, and the blue by a violet 

 colour. 



Nitroso-indol Reaction. Fuming nitric acid gives, with indol, a 

 deep red colour, or the reaction may be still better performed by 

 mixing the distillate with a drop of pure nitric acid and then carefully 

 adding a 2 per cent, solution of potassium nitrite. Skatol does not 

 give this so-called nitroso-indol reaction. 



The remainder of the distillate is shaken with ether in a separating 

 funnel. The ether dissolves out the aromatic bodies along with volatile 

 fatty acid. The ethereal extract is, accordingly, shaken with weak 

 caustic alkali which removes the fatty acid, and the purified ethereal 

 extract is slowly evaporated to dryness, the residue consisting of a 

 mixture of indol and skatol. 



CHAPTER IX 

 BILE. 



IN connection with the composition of bile, it is of importance to note 

 that the compound proteid which it contains is, in some animals e.g. 

 the ox nucleo-albumin, whereas in others e.g. man it is mucin. In 

 all cases it is probable that this proteid does not really come from the 



