MEDIA MAKING AND APPARATUS 269* 



1st. They include several media not mentioned in the schedule 

 of the Committee. 



2nd. For making gelatin, the water is added with the sheet 

 gelatin at Step 5 (c) above, instead of adding the water at Step 1 

 and the sheet gelatin at Step 5, as in the Committee schedule. 



3rd. In Step 4, the Committee specifies 6o° C. as the limit for 

 temperature in dissolving peptone. 



4th. The operations are described in somewhat greater detail. 

 None of these four changes are of moment except as contributing to 

 simplicity and uniformity of technique. 



'5th. The adjustment of reaction is made to precede, instead' 

 of, as in the Committee schedule, follow, the 30 minutes heating 

 on the water bath. 



6th. The period of boiling over free flame is given as 5 

 minutes instead of the 2 minutes in the Committee schedule. 



The changes 5 and 6 were suggested to the Committee and 

 accepted by them for reasons given in the writer's article (Journ. 

 Infec. Diseases, Supplement II, p. 223), but since no revision of the- 

 report has since been made, the schedule appears uncorrected m. 

 existing reports. 



Milk Medium. — Plain, fresh, rich milk (preferably " certi- 

 fied "), skimmed by centrifugalization, of a reaction not over 1.5% 

 (normal) acid, is to be brought to 1% (normal) acid, tubed and 

 sterilized. 



Litmus milk is prepared by adding to the above, before tubing, 

 1% of the litmus solution described below (or of a 2% aqueous 

 azolitmin solution, when this can be procured of the proper grade.) 



Artificial Milk. — (Lactose Nutrose Solution). — Owing to the 

 fact that milk has a varying acidity and to the inconvenience of 

 securing separator milk, which, when secured, is not wholly free 

 from fat, the following is offered as a substitute: Nutrose (Sodium 

 — phosphate — casein), 2.6 grams; lactose, 1.1 grams; water (dis- 

 tilled), 100 c.c. Heat slightly to dissolve the nutrose. Do not boil'. 



