113 



191 



6. In the pure lactic acid fermentation, the hexoses are simply split up into two 

 molecules of lactic acid; the pentoses, on the other hand, are not, as might be expected, 

 split up into one molecule of lactic acid and one molecule of acetic acid, but as a rule accor- 

 ding to the formula: 



eC^H.^O, = 8C3H,03 +3C2H,0, 

 6 pentoses = 8 lactic acid -f- 3 acetic acid, 

 which thus gives proportionately more lactic acid. 



7. The enzymes which hydrolyse the disaccharides appear to be endo-enzymes, and 

 we must therefore suppose that these sugars are taken in as such. There is consequently 

 nothing to prevent the disaccharides from being better nutriment than the monosacchar- 

 ides of which they are composed, and as regards the betacocci in particular, they can 

 form slime from cane sugar, but neither from dextrose nor from'lævulose, just as various 

 other lactic acid bacteria likewise form slime from lactose but neither from dextrose 

 nor from galactose. In the latter case, however, the nitrogenous nourishment is also of 

 importance, as the slime formation only occurs in milk. 



8. Of the four hexoses: lævulose, glucose, mannose and galactose, the last is as a rule 

 that which the lactic acid bacteria find most difficulty in fermenting. Some few species 

 however are altogether incapable of fermenting mannose, and will then often not attack 

 salicin either. In the case of some few species, the power of fermenting mannose and 

 that of fermenting arabinose are inversely proportional. 



9. Only saccharose-fermenting bacteria are able to ferment raffinose. Bacteria Which 

 ferment starch can also ferment glycogen, and vice versa. The same enzymes therefore, 

 are required to affect vegetable and animal starch. 



10. The true lactic acid bacteria never ferment gum arabic, erythrite and adonite, 

 and only rarely dulcite and inosite. The fermentation of the two last is in any case only 

 slight. ■ " 



11. In studying a bacteria, it is not sufficient merely to investigate which sugars 

 it ferments at all, but the quantity of acid formed must be estimated accurately in order 

 to determine in what order the different sugars are preferred. The order of preference 

 of the sources of energy is our most important means of identification but may however, 

 like any other character, lead to serious errors if employed alone. 



12. Only few lactic acid bacteria can thrive altogether without sugar, but all of them 

 grow as long as there is only a trace of sugar present. In the case of the streptococci, and 

 the tetracocci, the sugar optimum lies between — 2 %. .\n exception, however, is formed 

 by Streptococcus cremoris. Which, like the betacocci, prefers 5 — 10 °o sugar. The sugar 

 optimum of the rod forms lies between 2 — 5 °o- A sugar concentration of 2 °o is, however 

 in all cases extremely favourable. 



13. The lactic acid bacteria are as a rule but poorly supplied with proteolytic enzymes. 

 Some strains have no effect at all worth mentioning either upon peptones or casein (the 

 majority of betacocci, betabacteria and partly also of the species Streptobacteriiim plan- 

 /arum) ; others afïect peptones, but not casein (most of the streptococci, and all strains 

 of the species Tetracoccus casei); others again both peptones and casein (most of the tetra- 

 cocci and of the species Sc. lactis, Sc. cremoris, Sc. bovis and Sbn}. casei). The active en- 

 zymes are in all these cases endo-enzymes (probably erepsin), which act only in nearly 



D. K. D. Vidensk. Selsk. Skr., naturvldensk. og niathem. .Md. 8. R.-ekke. V. 2. 25 



