49 



Rrsii/f. -T\iii simple potiilo hroth f+'^'O powerfully retiirded the 

 oiowtli of Ps. liyachith'i^ the fluid renniining perfeetly clear for 8 

 duN'.s, aud probabh^ much longer. On the twent}' -fourth da}', when 

 next examined, the fluid was clouded, showed some precipitate and 

 had l)ccome alkaline. The +24 and +28 ))roths were both feebly 

 clouded in 72 hours. The peptone potato broth nuist have clouded 

 somewhat earlier than the last two, as it showed distinctly more 

 growth at the end of the third day. Query: What was the inhibiting 

 sul)stance represented b}^ the ditt'erence l)etween +30 and +28 and 

 removed Ijy the addition of this small amount of sodium hydrate? 

 Could it be oxalic acid? 



(2) The preceding experiment was repeated, all of the conditions 

 remaining the same, except that fewer germs were put into the tubes. 

 The inoculations were from an alkaline beef broth culture 12 days old, 

 and each tube received a moderate sized loop instead of a large loop. 



Rcsidt. — In the +30 broth, which was feel)ly acid to litnms, no 

 growth ever appeared (31 da3"s). In the +24 broth a very feeble 

 clouding was visible in 'o'^ hours. In the +28 broth clouding was 

 visible in 44 hours. Feeble clouding also appeared within 44 hours 

 in the peptone potato broth. 



A-, campeiitrh and Ps. phaseoU also refused to grow in the +30 

 broth. I*s. stewarti grew in it readily. 



Malic Acid. 



This acid was added to gelatins (see Nutrient gelatins) and to the 

 potato broth already described. A portion of this potato broth was 

 measured out and enough of this substance was added to raise the acidity 

 of the broth from +30 to +45. A tube was inoculated with a large loop 

 of /Iv. J( yd chit hi from the same culture used for the first potato-broth 

 experiments. The tube was exposed to the same favorable conditions 

 as the potato-broth tu})es, but no growth ever appeared (55 days). A 

 month later the experiment was repeated, inoculating with a moderate 

 sized loop from the culture used for the second potato-) )roth experi- 

 ments. This tube was subject to the same conditions as the latter, but 

 no growth ever appeared (31 days). A month later, 2 more tubes 

 were inoculated, using an enormous number of germs, viz, for each 

 tube a mass of l)right yellow slime 2 mm. in diameter, which was 

 taken from the fresh surface of a starch-jelh' culture It days old. 

 These well-plugged tubes were kept in ver}- feeble ditf used light, at 

 room temperatures of 23^ to 30^ C, but no growth ever appeared 

 (80 days). 



l*s. cainpestrix and Ps. phaseoli also refused to grow in this broth. 

 On the contrary, BacfUas amylovoriis^ inoculated from a colony, 

 clouded it in 48 hours and in the end made a better growth in it than 

 21788— No. 28—01 4 



