154 



76 



mine with certainty, as the tetracocci are on the whole but weak acid formers, and their 

 power of forming acid is easily weakened, so that we have all possible transitions between 

 acid formers and non-acid-formers. There is one point, however, which seems to suggest 

 that the two groups should be regarded as two distinct genera, viz. that all acid formers 

 are without exception more or less GnAM-positive, whereas non-acid-formers as a rule 

 are GnAM-negative. Winslow even goes so far as to divide all spherical bacteria into two 

 sub-families; the acid formers, or Paracoccaceæ, including my streptococci, betacocci and 

 tetracocci, and the non-acid-formers, or Meiacoccaceæ^). 



Genus: Tetracoccus (Abbr. Tc). 



In this genus (Table XXVII) I include all sugar-fermenting micrococci and sarcinæ. 

 From the sugar, they form, besides lactic acid, smaller or greater quantities of acetic acid. 

 The quantity of lactic acid was in many cases so small that we were not able to determine 

 with certainty of what sort it was. As they thus stand at the limit of what we will term 

 lactic acid bacteria, we have not sought for them systematically, as for the cocci 

 already described, and thus make no claim to have found, even approximately, represen- 

 tatives of all species belonging thereto, but merely of some of those most frequently met 

 with in the dairy. 



As already mentioned, our strains have been arranged according to their need of air 

 (see last column of the table), which I consider to be one of the best characters, even though 

 the surface growth of the stab cultures do not always assume quite the same dimensions, 

 and though a strain which at first exhibits no surface growth at all may in course of 

 years develop some surface growth, as happened in the case of No. 4. The strains which 

 spread most markedly on the surface, however, are found on the other hand to grow poorly 

 deeper down. In shaking cultures, the most aerobic forms grow only on or close under 

 the surface — and this even When the substrate contains sugar. Like the coli and aer- 

 ogenes bacteria, as a rule they spread more on the surface of sugar-free substrates (AG) 

 than on those containing sugar (SG). A small amount of sugar (but not more than ^/^%) 

 on the other hand will strengthen the colouring. This is, by the way, not a little variable, 

 and it is therefore very unfortunate that most of the bacteria coming under this head 

 have been named thereafter. There are, it is true, pure White forms, which never exhibit 

 any trace of colour, and the typical A ureus-f orms also are fairly constant in respect of 

 colouring, though the first generation may be a good deal paler, if sowing be done from the 

 bottom of the stab instead of from the upper part. In most strains, however, the colour 

 fluctuates, from one inoculation to another, between white, greenish, yellowish and brown- 

 ish. Slight alterations in the composition of the nutritive substrate will at once affect 

 the chromogenic power. Quite fresh cultures are often white, only becoming tinged after 

 a few days, or even weeks. . Some strains remain White for years together, and only 

 in a single generation exhibit a slight shading; others may be coloured, and then become 

 suddenly white. At times, the surface culture consists of white and coloured rings, or a 

 coloured star may form in the centre. On sowing out from tlie white and the coloured 



•) Systematic relationships of the Coccaceæ. New York 1908. 



