70 



Profs. H. Marshall Ward and J. Eeynolds Green. 



well in gentian violet by Gram's method, and were non-motile. At 

 23° and 20° C. the growth was similar bnt slower. 



Wort-agar, however, was unsuitable, cultures parallel with the above, 

 showing very slight growths at any temperature ; results quite conform- 

 able with previous experience. 



Here, again, we must conclude that the agar is of little or no import- 

 ance, except as a support. The significance of the failure on agar, to 

 which porcelain-filtered yeast extract and saccharose was added, appears 

 significant, and we shall return to this in order to discuss what happens 

 to the yeast extract and sugar when this mode of sterilisation alone is 

 relied on. 



Beer Wort. 



In beer wort (unhopped) the bacterium grows fairly well at first, 

 rapid turbidity following the infection, and a dirty yellowish deposit 

 soon falls, consisting of the flocculent bacterial masses carrying down 

 colouring matter ; but the liquid is not viscous, and the deposit scarcely 

 slimy, and growth soon ceases. 



When we reflect that beer wort — i.e., malt extract — is usually an 

 excellent medium for the growth of fungi, it is somewhat surprising 

 that this sugar-loving bacterium should do so badly in it. Thinking 

 that the failure might be owing to the kind of sugar in beer wort being 

 unsuitable, we tried adding saccharose, but no obvious improvement 

 was effected. We have seen (p. 69, above) that beer wort and gelatine 

 gave poor results, and we concluded provisionally that some unfavour- 

 able substance occurs in wort. 



Struck by the success of the preliminary trials with cane sugar, and 

 remembering the alleged original habitat of the organism, it was deter- 

 mined to try the effect of beet : this was done not only because beet 

 is a well-known source of cane sugar, but also because one of us had 

 previously observed in a certain beet disease, that a bacterium very 

 similar to the one under investigation spreads in the tissues of the 

 sugar-beet, and is connected in some way with the disease itself. 



Beet Extract. 



Cold water extract of crushed sugar-beet was found at an early stage 

 of the work to be a favourable medium. In tubes at 25° C, cultures 

 in carbon dioxide rapidly become- turbid, and on the third day, a dense 

 slimy zooglcea-like deposit had fallen to the bottom carrying with it the 

 colouring matters, and containing embedded bacteria. The same at 

 15° C. in carbon dioxide, the growth being simply somewhat slower. 



Parallel cultures — from the same tubes — in broth, gelatine, or agar, 

 devoid of sugars, showed no growth either in air or in carbon dioxide, 

 at 15° or at 25° C. 



