CH. VITI.] PTYALIN. 189 



His objection to the Achromic Point method is that 

 the end point is very difficult to determine, especially with 

 weak enzymes, and that the digestion (" chromic ") 

 period bears no simple relationship to the concentration 

 of the enzyme. This is undoubtedly well-founded, for 

 if the enzyme be halved the chromic period is more than 

 doubled. 



His objection to Wohlgemuth's method is mainly based 

 on the fact that in certain experiments the amounts of 

 enzyme added are in a geometrical series, and so the only 

 results obtainable will also be in a geometrical progression. 

 But this is a poor argument, for the experimenter can vary 

 the amount of enzyme added as he pleases. 



It is curious that neither Wohlgemuth nor Lovatt 

 Evans take any serious precautions to maintain the 

 optimum P H or salt content. In fact, certain results of 

 the latter with the Achromic method may be due in part 

 to the dilution of the chlorides of the saliva and not merely 

 to the dilution of the enzyme. 



After a considerable amount of investigation the 

 author has decided to adopt a colorimetric method for 

 ordinary work (see Ex. 242). It is by no means perfect, 

 but it is fairly rapid, and the end point is more easily 

 determined than in the Achromic or Wohlgemuth's 

 method. The relationship between amount of enzyme 

 and rate of digestion is fairly exact for moderate changes 

 in dilution. 



234. Obtain diluted saliva as follows : Warm some distilled 

 water in a beaker to about 40 C. With a portion of this thoroughly 

 rinse out the mouth. Now take about 20 cc. of the warm water 

 into the mouth and move it about by the tongue for at least a 

 minute. Collect the fluid thus obtained in a clean beaker, and 

 repeat the process once or twice, depending on the amount required. 

 Transfer the whole to a flask, close with the thumb, shake vigorously, 

 and filter. 



