THE NEW ENGLAND STATES. 25 



the agar medium, which is a variation on the recommendations of 

 the committee. The differences between the results obtained by the 

 use of agar containing sodium chlorid and those obtained with agar 

 having no salt appeared, in this investigation, to be very slight, but 

 further work is being done along this line. The reaction of the 

 finished medium is + 1 per cent to phenolphthalein. Agar medium 

 is generally sterilized in the autoclave under 15 pounds' pressure 

 (120 C.) for at least 15 minutes. When the intermittent method 

 is employed, the medium is exposed on three successive days for at 

 least 30 minutes, after the sterilizer is well filled with steam. After 

 sterilization all media are stored in the refrigerator to prevent changes 

 due to evaporation. 



Nutrient Iroth is prepared in the usual manner from digested lean 

 meat, 1 per cent peptone, and 0.5 per cent sodium chlorid; final 

 reactions + 1 per cent. 



Dextrose, lactose, and saccharose media are prepared by using Lie- 

 big's beef extract as a substitute for the lean beef bouillon; the final 

 reaction is neutral. Special sugar-free medium is obtained by inocu- 

 lating the meat infusion with B. coll. Sterilization is accomplished 

 by the intermittent process, except for dextrose, which is treated in 

 the autoclave. The ox-bile medium, as recommended by Jackson and 

 other members of the committee, 1 is now used in this laboratory as 

 routine procedure in all fermentation tests. This consists of ordinary 

 ox bile to which is added 1 per cent of peptone and 1 per cent of 

 lactose, placed in fermentation tubes (inverted or old-style pattern) 

 and sterilized. This is a very satisfactory medium. 



Differential media. Instead of lactose, or dextrose litmus agar, Mac- 

 Conkey's 2 bile salt agar was used for the isolation of B. coli like 

 organisms. After long experience with this medium this laboratory 

 has become familiar with various colony characteristics, and at pres- 

 ent it does not seem desirable to change the procedure, although it 

 is appreciated that many other workers obtain excellent results from 

 the use of Endo's medium, litmus agar, etc. The desired result is 

 obtained by either method employed, and the choice becomes largely 

 a matter of personal preference due to experience with the use of cer- 

 tain media. Agar medium prepared from calf's liver after the same 

 general formula as MacConkey's, but containing no added sodium 

 tautocholate, is being experimented upon as a differential medium. 



1 Second progress report of the Committee on Standard Methods for the Bacterial Examination of 

 Water and Sewage. Reprinted from the American Journal of Public Hygiene, v. 20, No. 3, August, 1910. 



2 Water (distilled) cc. . 1, 000 



Peptone ( Witte's) gin. . 20 



Lactose, c. p gin. . 10 



Agar (shredded and ground) gm. . 15 



Sodium taurocholate gm. . 5 



Color with neutral red, generally requiring about 5 cc of a 1 per cent solution per liter for desired tint. 



