48 



Lactic Acid. 



Schering's diabetinc (fructose) in 1 j^rani doses was added to test 

 tubes containing 10 c. c. portions of standard nutrient agar (acidity 

 + 15.5 of Fuller's scale), on which Ps. hyacintld was known to grow 

 well. This agar was resterilized, slanted, and inoculated b}- streak- 

 ing, but no growth could be obtained (58 days). The inoculation was 

 from an agar culture 13 days old, a large loop of the 3"ellow slime of 

 Ps. hyacinthl being rubbed thoroughly over the whole surface. That 

 the culture used for inoculation was alive was shown by the fact that an 

 inoculation therefrom into the san)e agar without the sugar produced 

 a decided growth in 24 hours. This fructose agar was distincth^ acid 

 to neutral litmus paper, owing presumably to the presence of a small 

 amount of lactic acid which is said by the manufacturers to be put into 

 the sugar to improve its keeping qualities. Ten grams of this sugar 

 required 10 c. c. of /„ NaOH to render it moderately alkaline to litmus. 

 When 0.7 c. c. and 1.0 c. c. portions of this alkaline sirup were added 

 to tubes of this agar a substratum was obtained on which, after a 

 time, the organism grew luxuriantly. The inoculations were made 

 with a loop of slime from solid cultures. In the 0.7 c. c. tubes, growth 

 was feeble during the first 4 or 5 days, then excellent and long-con- 

 tinued. In the 1.0 c. c. tubes, growth at the end of 7 da3\s was still 

 very feeble, i. e., not one one hundredth as much as in the tubes 

 containing onl}'^ seven-tenths as much of the alkaline sugar. On the 

 twelfth da}" there was about one-third as much growth; on the six- 

 teenth day growth had much increased. After this the 2 sets of tubes 

 looked much alike and the growth was at least 10 times as abundant 

 as on the same agar without the sugar. 



Potato Broth. 



This broth was half strength, i. e., VA. It was made by putting 500 

 grams of thinly sliced potatoes into 1,000 c. c. of distilled water 

 and heating on a water bath 2 hours at 10° to 55^^ C. The broth was 

 then filtered, steamed one hour, cooled, made up to 2,000 c. c, filtered, 

 tirated, and divided. Its acidity was +30 of Fuller's scale. For 

 comparison, a portion of this l)roth received enough caustic soda to 

 make it +24, another portion received one-third as much soda and 

 registered an acidity of +2S, a third portion received 1 per cent of 

 Witte's peptonum siccum. This last was not titrated, but the peptone 

 is known to give an alkaline reaction with litmus, and this addition 

 must have considerably reduced the acidit}' of the fluid. 



(1) Each tube contained 10 c. c. of ])roth and was well plugged. 

 All were inoculated at the same time and were kept together in feeble 

 diffused light, at room temperatures ranging from 20'^ to 25^^ C. Each 

 tu])e was inoculated with a large loop from a well clouded alkaline 

 beef broth culture 11 days old. 



