85 



163 



toria of milk attack all casein strongly, with direct fornialion of mono-aniino-acids, and 

 they are therefore of importance in the ripening of the cooked sorts of cheese, which 

 arc not till 24 hours after cooled below the temperatures most favourable for develop- 

 ment of thermobacteria. No. 12 in particular is of the greatest importance in the rijjen- 

 ing of Swiss cheese (Emmental cheese)^). 



The thermobacteria do not as a rule care for [)entoses and alcohols. Only No. 6, 

 which is further distinguished by being able to ferment inulin, exhibits any considerable 

 fermentation of mannite. Most of the mash bacteria do not ferment galactose and lactose, 

 and the two yoghurt bacteria do not ferment maltose. Saccharose is not fermented by 

 Nos. 1, 2, 12, 13 and 14. The maltose-fermenting thermobacteria as a rule also ferment 

 some dextrin, and often also a small quantity of starch, besides raffinose and salicin. 

 Yeast extract will at first retard the growth of the yoghurt bacteria, and can thereby 

 prevent them altogether from attaining development in certain sugars (lactose, for in- 

 stance). There is altogether something capricious in the attitude of the thermobacteria 

 towards the sugars, due to the fact that our artificial substrates did not entirely satisfy 

 their needs^). 



The thermobacteria (PI. XXVIII — XXXIV) are pronounced long-rod forms, with 

 a tendency to grow out into threads, often strangely curling. They consist, however, 

 of several segments, which is not to be seen in the water preparation, but is distinctly 

 apparent when the preparation is laid in Canada balsam (See PI. XXXII). In a young and 

 vigourous state, they occur for the most part singly, or two and two. As they are seriously 

 affected by the oxygen in the air, they assume irregular shapes in streak cultures. Mere, 

 they always form an extremely thin layer, and some few (as No. 14, for instance) do not 

 grow on the surface at all. When stained with methylene blue, they generally prove to 

 contain volutin grains. No. 13 does not appear to form grains, and No. 12 but rarely. 

 The granular formation is most marked in No. 14 (PI. XXXIII), which is also in German 

 often called Körnchenbazillus. With some strains, most grains are found in the quite 

 young rods (No. 14 for instance); in other strains, again, in rods 2 — 3 days old (as No. 6 

 PI. XXIX) and the size and shape of the grains depends to a high degree upon the nutri- 

 tive substrate. In the case of No. 14, the mere fact that the milk used had been heated 

 some few degrees more or less is sufficient to alter the picture entirely. Normally, this 

 yoghurt rod, when stained with methylene blue, has round, dark-blue grains, and no 

 capsule; when cultivated in pasteurised milk, on the other hand (and especially in milk 

 heated for half an hour to 80°) it has oblong red grains and distinct capsule (PI. XXXIII). 

 According to Gram, Nos. 12 (Pl. XXXI) and 13 (Pl. XXXII) are not stained completely, 

 but exhibit a quantity of irregular granules. Something similar may be observed in the 

 case of other thermobacteria, if very old for instance, or if stained in a too acid state. 

 As these bacteria are such strong acid-formers, it is altogether best first to neutralise 

 the cultures to be used for colour preparations. The thermobacteria are often over 1 ^ 

 thick. In old cultures, they can develop greatly swollen or otherwise involved forms. 



') See further in my Dairy Bacteriology 1916, p. 112. 



■) This explains certain points of difference with other writers. Barthel (1. c.i, for instance, lias 

 found that the identical strain No. 12, which we have worked with, ferments mannite and a small 

 quantity of saccharose, which we iiave never been ai)le to observe. 



