17S 



100 



of acidity will rise very slowly in the remaining kefir, and in pure cultures, the kefir rods 

 form no acid in milk. Bbm. caucasicum grows altogether slowly as a pure culture. It 

 thrives best in yeast extract, and its powerful growth in kefir grains must therefore be 

 due to a symbiontic relation to the yeast cells therein. After cultivation for many years 

 in casein peptone, however, it can become so accustomed to this source of nitrogen, that 

 it will ferment the same sugars with this as with yeast extract (see No. 2). Of all the' 

 betabacteria, Bbm. caucasicum is the most pronounced A-form, as with less suitable 

 nitrogen sources it will only ferment arabinose at all, and if tested therefore, under these 

 circumstances. With all other sugars than arabinose in particular, one must necessarily 

 conclude that it does not belong to the lactic acid bacteria. 



Bbm. caucasicum forms shorter or longer rods, which are apt to clump together, in 

 broth and milk, to miniature kefir grains (PI. XLV I). Large kefir grains, however, I have 

 never succeeded in producing with pure cultures. In the true grains, the rods are often 

 very long and curved, and tangled together. In highly acid cultures the kefir rods can, 

 after treatment with methylene blue, exhibit unstained parts, which have previously 

 been regarded as spores (Dispora). 



Botabacterium breve, has its optimal temperature at 30°. It thrives very badly below 

 15° and above 37^2°- It grows somewhat better than the streptobacteria on sugar ge- 

 latin. 



Bbm. breve has not only difficulty in fermenting mannose, but some few strains 

 (Nos. 8 and 9, and With bad sources of nitrogen also Nos. 5, 6 and 10) have a relatively 

 low fermentation of lævulose, and, which is still more remarkable, other strains (Nos. 13, 

 14, 15, 16 and 17) even find it difficult to utilise dextrose. The fermentation of galactose 

 is as a rule on a level with that of dextrose, and We can therefore — in contrast to what 

 we have otherwise seen in the case of the lactic acid bacteria — find strains which fer- 

 ment galactose considerably more strongly than lævulose. Only few strains ferment 

 saccharose or raffinose. As with the betacocci, the power of fermenting maltose and 

 lactose has in many strains perceptibly decreased during the time we have had them 

 under cultivation. We find altogether something of the same variability as in the beta- 

 cocci, which renders the line of demarcation between Bbm. breve and Bbm. longum some- 

 what vague. 



Bbm. breve {P\. XLVI-XLVIII) occurs most frequently in the form of regular, isolated 

 rods with rounded ends. The most common size is 0.7 — 1 x 2 — 4 //. Chains of short segments 

 are, however, found, especially in broth at the first stage of development (No. 3, PI. 

 XLV II). Later on, the segments become longer, and fall away from one another. Only 

 a single strain (No. 8, PI. XLVII) forms rings similar to those often seen in certain strepto- 

 bacteria. When stained with methylene blue, several strains exhibit the granulation so 

 characteristic of the thermobacteria. 



Betabacterium longum grows most rapidly at a couple of degrees below its maximal 

 temperature, which lies about 45°. It does not develop at anything under 18°. A number 

 of strains ferment xylose, but none arabinose. As a rule, it ferments saccharose and raffi- 

 nose. It often forms long rods (No. 33, PI. XLVII I) which can resemble those of the ther- 

 mobacteria. Generally, however, they exhibit no granulation, when stained with methy- 

 lene blue. In a few strains (see photos of No. 22) the rods ore inclined to develop irregular 

 swellings. 



