56 



pared with the lactose broth medium employed in the Public Health Ser- 

 vice. 



The Public Health Service lactose broth is made as follows: Nutrient 

 broth neutral to phenophthalein is prepared in bulk and sterilized in the 

 autoclave. A sufficient quantity of a 20 percent solution of lactose in 

 distilled water, previously sterilized in the Arnold for an hour and a half, 

 is then added to make a concentration of 1 percent. The medium is then 

 distributed aseptically into sterile Smith fermentation tubes, which are 

 then heated in the Arnold for 30 minutes. 



Hasseltine found that the "Standard" lactose broth gave 73 percent more 

 positive fermentations and yielded 10 percent fewer confirmations than the 

 Public Health Service medium. With reference to these observations, it 

 should be pointed out, however, that in the preparation of the Standard 

 broth, the period of sterilization was quite prolonged. He states that the 

 broth was in the autoclave for about an hour (25 minutes to raise the 

 pressure to 15 pounds, 15 minutes at that pressure, and about 20 minutes 

 to allow the pressure to fall sufficiently to permit opening the autoclave 

 without blowing out or wetting the stoppers). In the autoclave in which 

 steam must be generated this prolonged period is of course probably neces- 

 sary but in autoclaves provided with pressure steam, the entire period of 

 sterilization may be reduced to 25 or at most 30 minutes; with such an 

 instrument, the very significant objections raised by Hasseltine do not 

 apply. In fact, Mudge, in a careful study of the relative effects of tem- 

 perature and pressure as compared with time of exposure, concludes that 

 the time factor is the more vital one in the decomposition of lactose. He 

 maintains that heating in streaming steam for three successive days, as is 

 ordinarily done in the Arnold, will cause a greater hydrolysis of lactose and 

 maltose than sterilization in the autoclave at 15 pounds for 15 minutes. 

 These conclusions are based upon the relative increase in monosaccharids 

 as indicated in Table XXV. By use of bacterial cultures confirmatory re- 

 sults were obtained. 



TABLE XXV. EFFECT OF METHOD OF STERILIZATION ON DECOMPOSITION 



OF CARBOHYDRATES. 

 (After Mudge 1917) 



*Figures indicate relative degree of reduction as determined by Barfoed's method 

 for monosac,charids. . 



Mudge also makes an interesting observation as to the cause of in- 

 creased acidity in sterilized culture media. As is well known, a neutral 



