Rod Forms. 



The rod-shaped lactic acid bacteria are on the whole stronger acid-formers than the 

 spherical, and this is most distinctly apparent "when yeast extract is used as source of 

 nitrogen. If they grow at all on gelatin plates, the colonies are as a rule not visible until 

 after the lapse of 5 — 6 days. They fall into three well characterised genera; Thennobacler- 

 ium, Sirepiobaderium and Belabaderium. Of these, the thermobacteria, which do not 

 grow at ordinary temperature are more anaerobic than the other lactic acid bacteria, 

 whereas the streptobacteria and the betabacteria behave towards the oxygen of the air 

 — as indeed towards most other things — like the corresponding streptococci and betacocci. 

 The streptobacteria do not develop gas, and always ferment salicin; the betabacteria, 

 on the other hand, develop more or less gas, and never ferment salicin. Finally, to the 

 rod-shaped lactic acid bacteria should be added some small rods, the genus Microbaderium, 

 which, however, differs quite as much from the true lactic acid bacteria as the tetracocci. 

 Among the microbacteria should possibly be reckoned the Bacillus addophilus often men- 

 tioned in medical works. And in conclusion, we should mention Badllus bifidus, as being 

 — ■ albeit without further justification — generally reckoned as belonging to the rod- 

 shaped lactic acid bacteria. 



Genus: Thermobacterium (Abbr. Tbm.). 



The thermobacteria are as a rule not killed by heating until a temperature of over 

 75° has been reached, they also require, as their name implies, a high temperature for their 

 development. With the exception of No. 8 (Table XVIII) which grows at 18°, none of the 

 strains investigated develop at anything below 20° — 22°, and even at 30° the growth 

 is very slow. Therefore they will not grow in gelatin plates. The optimal temperature 

 lies about 40°, and here the growth proceeds at a furious rate, as long as the strains are not 

 weakened from any cause. The maximal temperature is as a rule 50°; Tmb. bulgancum 

 (No. 14) grows at 52^/2°, and the mash bacteria at even higher temperatures, as is known 

 from the distilleries. The method of enriching thermobacteria in milk or mash is therefore 

 to let the liquids stand at temperatures between 47° and 54°. They may likewise be forced 

 in fresh cheese mass which is strongly heated (cooked). 



These bacteria are quite extraordinarily particular in respect of the nutritive sub- 

 strate they require, and we have not succeeded in producing artificial substrates whicli 



