102 BACTERIOLOaiCAL AND ENZYME CHEMISTRY • 



which will enable us to study the action of this enzyme upon 

 starch and thereby to obtain a knowledge of the conditions 

 of enzyme action in general. 



In the first place it will be necessary to prepare some 

 malt extract, and it may here at once be stated that it is of 

 fundamental importance in all work connected with the 

 preparation and study of enzymes that the conditions of 

 experiment should be very carefully under control, more 

 especially the temperature. For this purpose constant- 

 temperature incubators (see Fig. 7) are essential. It is also 

 better to use constant temperature water-baths ; Fig. 4 b shows 

 a convenient type of water-bath for this kind of work. Small 

 beakers capable of holding conveniently about 100 c.c. of 

 solution can be fitted neatly into this bath by means of flat 

 rings ; test-tubes can also be held in position, or stacked in 

 the beakers. 



To prepare a cold water extract of malt 100 grams of 

 ground malt are mixed with 250 c.c. of water and the mixture 

 allowed to stand with frequent stirring for about five hours. 

 For the purpose of grinding the malt a small hand-mill similar 

 to a coffee grinding mill can be used. 



The various starches differ considerably in the ease with 

 which they are attacked by amylase, and for the purpose of 

 experiment it is better to use so-called soluble starch, which 

 is prepared after the manner described below, i 



' Cf. Brow a, Laboratory Studies, p. 65. Preparation of Soluble Starch. — 

 Introduce about fifty grams, of potato starch into a 500 c.c. flask, and half 

 fill the flask with a 7 '5 per cent, solution of hydrochloric acid made by 

 diluting 125 c.c. of the concentrated acid to 500 c.c. with distilled water. 

 Allow the starch to digest with the dilute acid at the ordinary room tempera- 

 ture for seven or eight days. The acid should then be poured off and the 

 starch washed repeatedly with distilled water by decantation until the 

 granules no longer give an acid reaction when placed on blue litmus-paper. 

 One or two drops of dilute ammonia should then be added, and the starch 

 again washed until every trace of ammonia is removed. Drain the starch 

 thoroughly on a filter, and spread it on filter-paper to air-dry at a temperature 

 of about 25° C. (77° F.). 



