264 



BACTERIA IN RELATION TO PLANT DISEASES. 



had reddened. On the surface of the agar a greedy aerobe was then sown (Bacillus subtilis) 

 with the idea that if an anaerobe were present in the milk it would develop in the depths of 

 the agar, whereas if only Bad. solanacearum were present the growth would not appear along 

 the line of the stab or would occur only in the top of the stab. The second of these supposi- 

 tions proved to be the true one, indicating that the litmus-milk cultures which reddened 

 contained only an aerobe, viz, the Medan organism. Owing to the fact that the media which 

 reddened had been made from uncentrifuged milk containing cream, whereas our ordi- 

 nary litmus milk is always made with centrifuged cream-free milk, it then seemed likely 

 that the acid must be due to the action of the bacteria upon the cream, not on the milk sugar, 

 and this was borne out by subsequent tests. When we inoculated skimmed (cream-free) lit- 

 mus milk we always got a gradual blueing of the litmus, just as in case of the American organ- 

 ism, and never any subsequent reddening. On the contrary, whenever we added cream to the 

 skimmed milk or prepared the litmus milk 

 out of milk containing cream, we got a red- 

 dening which began always in the layer of 

 cream at the top and gradually progressed 

 until the whole tube became reddened (pi. 

 44, figs. 2, 3, 4). There can be no doubt I 

 think, therefore, that the discrepancy be- 

 tween Honing's results and my own is not 

 a real one. The Medan organism, like 

 the American one, blues cream-free litmus 

 milk. The Medan one reddens mixtures 

 of cream and milk containing litmus, and 

 probably the American tobacco organism 

 would do the same thing, although we 

 have not tested it.* 



In repeated tests we have never ob- 

 served any reddening in cream-free litmus 

 milk, using Honing's organism, but al- 

 ways a reddening when cream was added. 

 Coconut oil added to cream-free lit- 

 mus milk is also split by Medan III with 

 the production of an acid, but under the 

 same conditions no acid was produced 

 from olive oil, peanut oil, or cottonseed oil. 



Whenever a 

 thin layer of sterile 

 cream, paraffin, or 

 any of the above- 

 mentioned oils was 

 placed on the sur- 



face of the inocu- 

 lated litmus-milk, 



Fig. 134i.{ 



Fig. I34o.f 



so as to interfere with the absorption of 



oxygen, there ensued a distinct reduction of the litmus, but this reduction was not observed 

 when the surface of the litmus milk was freely exposed to the air then the lavender blue 

 milk became and remained a uniform deep blue. 



*Thc only American strain I have tested is the Florida potato organism (1914): This does not redden creamed 

 litmus milk. In each of 4 trials the numerous inoculated tubes became and remained bluer than the checks. At the 

 end of 2 weeks this strain had grown well In Uschinsky's solution and very feebly in Cohn's solution. It is motile. 



tFio. 1340. Flagclla of Sumatran tobacco organism. Culture received from Honing. 



JFio. 1346. Young tobacco plant wilted by motile bacteria, a check on FIG. 1340, i. e., from the same culture. 



