Micrococci and Sarcinæ. 



As already mentioned, there are certain streptococci and betacocci which can appear 

 as typical micrococci or divide in several directions. And again, several of the micrococci 

 can stretch prior to division, or form short chains, thus resembling the foregoing families. 

 We cannot therefore, on morphological grounds alone, distinguish the micrococci from 

 these. In cultural respects, however, the micrococci and the Sarcinæ are both, as a rule, 

 easily distinguishable by the fact that on gelatin plates, they form larger — often coloured 

 — colonies, and in agar stab, growth on the surface. This quality also differs in the different 

 species, and in the accompanying tab'e (XXVII a and b), we have arranged our 

 strains with particular regard to their more or less pronounced need of air. The four first 

 (Nos. 1 — 4), it will be noticed, exhibit no surface growth at all, and thus present no diffe- 

 rence in cultural respects from the streptococci and betacocci, whereas the last (Nos. 30 — 

 31) form a thin wrinkled, mycoderma-like membrane. In contrast to the truer lactic 

 acid bacteria, however, the micrococci and sarcinæ are furnished with catalase, so that 

 their broth cultures give a development of oxygen with peroxide of hydrogen, — almost 

 always of the nature of an explosion — and this reaction is therefore a reliable charac- 

 ter by which to distinguish them from the other cocci, and especially from the micro- 

 coccus-like betacocci. 



* As the micrococci on the one hand, in morphological respects pass over by gradual 

 transition into the streptococci and betacocci, so, on the other hand, we find no sharply 

 distinct line of demarcation between the micrococci and sarcinæ. From our investigations, 

 we have reason to suppose that both these groups can divide in all three directions, but 

 the typical pachet only arises where there is a strong cohesion between the cells after 

 division. In the micrococci, this cohesion is as a rule but slight, and they therefore appear 

 most frequently as diplococci or in a grape-cluster form (as staphylococci) without any 

 pronounced direction for division; in the sarcinæ, on the other hand, it is generally stronger, 

 and we find these, accordingly, far more often than the micrococci, forming tetrads, and 

 now and again even distinct pachets. As micrococci and sarcinæ exhibit no differences 

 in biological respects, it is altogether unjustifiable to set them up as two distinct genera; 

 the dilïerence between them is not greater than between short- and long-chained strepto- 

 cocci; we therefore suggest the generic name Tetracoccus îor both groups. Micrococcus 

 ti in any case meaningless as a generic name, since the micrococci are by no means smaller 

 shan the other spherical bacteria. 



In the present work, we have only devoted attention to the sugar-fermenting strains. 

 Whether those which do not ferment sugar form another genus, we are not able to deter- 



20* 



