162 



84 



can altogether replace the natural milk or (non-sterilised) mash. For the milk bacteria, 

 vvhey-yeast-extract-agar. was found best. With the exception of No. 6, (which in contrast 

 to the other thermobacteria grows well with Witte peptone as nitrogen food, and which 

 we have also kept alive in casein peptone for a couple of years without re-inoculation) 

 they cannot be transferred every time from agar to agar, but often require a passage of 

 milk, or they will be weakened. Nos. 12, 13 and 14 should best be constantly transferred 

 from milk to milk. If chalk be added to the milk and the mixture be shaken up now and 

 again, the bacteria will retain their vitality unimpaired for several months, but When 

 using milk Mdthout chalk, it will bebest to re-inoculate each Week. No. 12 will however, 

 even under these conditions, keep unimpaired for several months at 15° and remain alive 

 for up to two months at 20°, though it will after a time be perceptibly weakened. No. 13, 

 which is probably identical with the yoghurt bacterium first described by Bertrand 

 and ^^'EISSWEILER^), since it forms similar pennete colonies, I did not succeed at all 

 in transferring from one artihcial substrate to another. It only takes on artificial sub- 

 strates when coming directly from the milk 2). The lactose-fermenting thermobacteria of 

 mash does not form acid in milk; the maltose-fermenting thermobacteria of milk, on 

 the other hand, thrive well enough in mash. For mash bacteria, a sterilised malt extract 

 solution is not nearly as good a nutritive substrate as might be supposed, owing to the 

 fact that an essential quantity of the nitrogenous substances therein contained are pre- 

 cipitated on sterilisation. An addition of yeast extract renders it more suitable, and we 

 have found that a solution of the trade malt extract (with abt. 50 % maltose and 0,5 % 

 N) to 7 parts of yeast extract (with 0,5 % A') gives a good nutritive substrate, with the 

 sugar concentration most favourable for these bacteria (see Table II d). Stab cultures in 

 high layers of an agar thus prepared are a good form for preservation. 



The lactic acid formed by thermobacteria is as a rule lævo-lactic, more rarely (Nos. 12 

 and 13) inactive. In addition to lactic acid, they form some acetic acid, and, as Barthel 

 first showed, a trace of succinic acid^). In powerful milk cultures of the thermobacteria 

 of milk, there is often so much gas produced that the curd exhibits fine stripes, and the 

 quantity of lactic acid rises to 1 Y-, %; for inactive acid indeed, even up to 2% %, which 

 is far in excess of the amount of lactic acid formed by other lactic acid bacteria. 



The thermobacteria of milk can under certain circumstances easily become slime- 

 formers. Btjrri and Thöni have shown, for instance, that No. 12 as a rule becomes slimy 

 when it has been cultivated for any length of time together with a certain mycoderma 

 species*). The slimy varieties are just as powerful acid formers as the non-slimy ones. 

 We have a slimy variety of No. 13 (presented by Mr. Blichfeldt, manager of the laboratory 

 of Monsted's Margarine factory, in England), which, in contrast to the streptococci, so 

 strongly retains its power of forming slime that even after long cultivation at high tem- 

 peratures we did not succeed in transferring it to a non-slimy variety. The thermobac- 



') Annales de l'Institut Pasteur 1906, Bd. 20, p. 977 



We have not, however, tried tlie malt germ decoction suggested bj' Bertrand and Duchacek • 

 (Biochemische Zeitschrift 1909, 20. Bd, p. 102 . 



Meddelande Nr. 69 från Centralanstalten for .lordbruksförsök. Stockholm 1912. 

 *i Landwirtschaftliches Jahrbuch der Schweiz, 1909, p. 271. 



