METHOD OF DESCRIBING CULTURES 65 



the discolorization of the litmus, whether this be pink or bhie. 

 This is due to the fact that the organism takes up the oxygen 

 necessary to maintain the coloration. It may be frequently 

 observed that at the surface, where atmospheric oxygen has 

 access, the color remains or is restored. The color may also be 

 restored by shaking the milk vigorously, thus bringing it into 

 intimate touch with the oxygen of the air. 



The production of a diastatic enzym (diastase, amylase) is 

 demonstrated by gas-production on potatoes. This medium con- 

 tains starch in large amounts. The starch is inverted into glu- 

 cose by diastase (amylase), and this is then fermented with 

 gas-production. 



Directions for filling out second page of culture-charts — 

 I . Note the reaction of the medium by the sign -|- for 

 acid and — for alkali reaction. 



2. The incubation temperature may be (a) 37" 

 (thermostat), (6) room temperature, (c) ice-chest. 



3. Plates are to be described only once after 24 or 

 48 hours, according to growth. Make notes in the first 

 column for gelatin; in the second, for agar-plate, writing 

 across the full width of the page. Make sketches in the 

 special column reserved for this purpose. 



4. The growth on the media 3, 4, 5, 6, 7, and 8 

 (enter here: " glucose-agar " only unless otherwise 

 instructed) to be made fully according to the outline in 

 the spaces under 24 hours. In the spaces under 48 hours 

 and 6 days note only the changes from the first day. 



5. Make sketches frequently and accurately, espe- 

 cially from milk and gelatin media, and any other remark- 

 able growth, in the column reserved for this purpose; 

 also a sketch of each organism from a part of a field 

 under the microscope. 



It is well to understand that these directions for fill- 



