116 



removed, and, after cooling to about 60 C., the white of one egg mixed 

 with a little distilled water is added. The contents are coagulated by 

 heating in current steam in the usual way, filtered, and the filtrate made 

 up to 1 liter. The mixture is made neutral, litmus paper being used as 

 the indicator. Then 19 c. c. of normal sodium carbonate solution and 

 10 grams of chemically pure lactose are added. The flask is replaced for 

 30 minutes in the steam sterilizer. Almost invariably there is a consider- 

 able precipitate, and the mixture has to be again filtered. 



2. Seven c. c. of the fuchsin solution (see below) are added, fol- 

 lowed by 25 c. c. of a quite freshly prepared 10 percent sodium sulphite 

 solution. The mixture becomes much less red, but is not immediately 

 decolorized. It is then tubed, conveniently into small flasks, each con- 

 taining 50 to 60 c. c. of media, and sterilized in current steam for two 

 days, 30 minutes each day. 



3. The fuchsin solution is made as follows: Three grams of pow- 

 dered crystalline fuchsin are placed in a dry flask, and 60 c. c. of abso- 

 lute alcohol are added. The contents are thoroughly mixed, and the flask, 

 tightly stoppered, allowed to stand for exactly 24 hours at 20 to 22 C. 

 The alcoholic extract is then decanted and preserved in a clean glass-stop- 

 pered bottle. Made in this way a uniform fuchsin extract is obtained 

 which keeps well, and the same quantity of fuchsin is added each time a 

 fresh batch of medium is prepared; a matter of much importance. 



The medium must be stored in the dark, since light gradually turns 

 it red. When solidified it is almost free from color. 



(h.) Conradi-Drigalski Agar (After Prescott and Winslow) These 

 authors have modified lactose litmus agar by adding to it nutrose and 

 crystal violet and by using three percent of agar instead of one percent. 

 The crystal violet strongly inhibits the growth of many other bacteria, es- 

 pecially cocci, which would also color the medium red; the 3 percent 

 agar makes the diffusion of the acid which is formed more difficult. 



Three pounds of chopped beef are allowed to stand 24 hours with 

 two liters of water. The meat infusion is boiled one hour and filtered. 

 Twenty gm. of Witte's peptone, 20 gm. of nutrose, and 10 gm. of NaCl 

 are then added, and the mixture boiled another hour. After filtration 

 and the addition of 60 gm. of agar the mixture is boiled for three hours, 

 made alkaline and filtered. In the meantime 300 c. c. of litmus solution 

 (Kahlbaum) are boiled for 15 minutes with 30 gm. of lactose. Both 

 solutions are then mixed and the mixture, which is now red, made faintly 

 alkaline with 10 percent soda solution. To this feebly alkaline mixture 

 4 c. c. of hot sterile 10 percent soda solution are added and 20 c. c. of a 

 sterile solution (1 to 1000) of crystal violet (Hochst B.). 



(i) Bile Salt (Rebipel) Agar (After Savage). Sodium tauro- 

 cholate 5 grams, Witte's peptone 20 grams, and distilled water 1 liter, 

 are boiled up together, 20 grams of agar are- added and dissolved in the 

 solution in the autoclave in the ordinary way. The medium is cleared with 

 white of egg and filtered. After filtration, 10 grams of lactose and 5 



