110 



32 



tn sugarless broth, Nvhen they have good sources of nitrogen at their disposal^). The lac- 

 tic acid bacteria are far more difficult to satisfy in respect of nitrogenous nourishment, 

 and it will be seen from Table IX, that several strains are unable to ferment grape sugar, 

 if they have only 14% Witte peptone available. Their demands in regard to nitrogenous 

 food are further increased when dealing with sugars more difficult of fermentation, such 

 as for instance inulin, which is often only affected when certain definite sources of nitrogen 

 are present. Only when the nitrogenous nourishment is in all respects sufficient lactic acid 

 bacteria are able to produce the numerous different enzymes (invertase, maltase, lactase, 

 inulinase, etc.) which are required to decompose the di- and polysaccharides-). It is there- 

 fore absolutely necessary to know the best sources of nitrogen for the 

 different bacteria, before proceeding to investigate which sugars they 

 are able to ferment at all. In the various tables for the different species of bacteria 

 it will be seen how greatly the source of nitrogen may affect the fermentation of the sugar. 

 We wiU especially draw attention to Streptococcus bovis Xos. 1 and 2 (Table XVIII). 

 Bctabacleriuin breve No. 11 (Table XXXI), Microbacterium laclicum No. 2 (Tab. XXXll) 

 and the many strains of Streptobacterium plantarum (Table XXX), which are particularly 

 susceptible as regards nitrogenous food. In all our earlier investigations with the lactic 

 acid bacteria, Witte pepton was our sole source of nitrogen, but even after we had found 

 other and better sources, we continued nevertheless to employ Witte peptone in addition, 

 as it is only by studying the fermentation of sugar as well with good 

 as with bad sources of nitrogen that it is possible to obtain a proper 

 impression as to which sugars the various strains prefer. The aerogenes bac- 

 teria are here, as in most other respects, found to take up a reverse position to the true 

 lactic acid bacteria, as they will most easily render the nutritive substrate alkaline with 

 the sugars which they find it most easj" to ferment, and as a matter of fact, it is only with 

 a slight quantity of nitrogenous nourishment that we can form any estimate as to which 

 sugars they ferment, unless by measuring the quantitites of gas developed, which is the 

 only rational method when dealing with these bacteria. 



■fhe lactic acid bacteria use their carbonic food chiefly as a source of energy, and 

 consequently throw off therefrom a quantity of breaking down products (fermentation 

 l)roducts); their nitrogenous nourishment, on the other hand, is employed princijjally 

 as building material, so that they do not need to give off any considerable amount of 

 breaking down products. As a rule, no perceptible decomposition of nitrogenous matters 

 takes place at all, unless the bacteria are suffered to continue their vital activity for some 

 length of lime, and it can only be occasioned by gradual neutralisation of the acid as it 

 is formed. Cultures in which it is required to study the decomposition of nitrogenous 



M In tfiis respect, however, there is a very essential difference between true and pseudo lactic 

 acid bacteria, as the latter — at any rate under aerobic conditions — always thrive excellently in 

 sugar-free peptone solutions. 



-I It is not unlikely that the entire question of vitamins, of which I have recently given a su^^•ey 

 in "Naturens Verden ' 1917. also has some connection with the enzyme ])roduction of the organisms. 

 Jacohy for instance, has shown :Bichem. Zeitschr. 1918, Bd. 86, p. 329) that the formation of urease In 

 bacteria capable of sphtting up urea is greatly furthered by the presence of a certaiu aniino-acid. 

 to wit, leucin. 



