88 



10 



In staining lactic acid bacteria, their acid content cannot always be disregarded. 

 Methylene blue, for instance, will not colour highly acid broth cultures at all. Instead of 

 adding alkali to the staining material, which may easily overcolour the preparation, it 

 is better to neutralise the culture employed. In making Indian ink preparations, which 

 give the best microphotographs, such neutralisation is also necessary in order to prevent 

 the colloid ink from flaking. 



The illustrations in the album are, where not otherwise stated, invariably Indian ink 

 preparations, magnified 1000 times; 500 times by means of the microscope, and twice 

 again by the camera. We have therefore considered it superfluous to note the size of the 

 lactic acid bacteria in the text; as a rule, they are from 0,7 to 1 ^ think. A few small rod 

 forms are exceptions; these We have called microbacteria (genus Microbaderium, PI. 

 XLIX — L) from their small size. It should be noted, however, that the apparent thickness 

 of the bacteria is affected by the thickness of the layer of Indian ink, wherefore the latter 

 should be applied as thinly as possible. In photographing and development also, the dimen- 

 sions may be affected, so that unless the microphotographs are constantly subjected to 

 careful control, they may turn out entirely misleading. When dealing with coloured pre- 

 parations, it should be borne in mind that only the protoplasm, without the cell wall, 

 is visible. Only capsule preparations give a thoroughly correct impression of the size of 

 the bacteria. These preparations are generally photographed in water, while the other 

 preparations are generally made in Canada balsam. 



A more detailed description of the morpholigical features can only be given when 

 dealing with the separate species. The variety of forms within the present group is in reality 

 so great that nothing can generally be said beyond what has already been mentioned. A 

 glance at the album will show us streptococci which divide in two directions {Sc. cremoris 

 Nr. 20, PI. VIII, Be. bovis No. 46, PI. XXIV) or form rods (Sc. thermophilus No. 2, PI. 

 XII, Be. bovis No. 33, PI. XXIII) and rods, which form streptococcus-like chains {Sbm. 

 easei No. 9, PI. XXXVII, No. 28, PI. XXXVIII, Sbm. planlarum No. 44, PI. XLV, Bbm. 

 breve No. 3, PI. XLVII) or more or less distinct screws {Sbm. easei No. 2, PI. XXXV, No. 

 33, PI. XXXIX, No. 34, PI. XL. Sbm. plantamm No. 1, PI. XLI and Bbm. breve No. 8, PI. 

 XLVII). These transition forms best show how futile it would be to take the shape of the 

 cell as a basis for dividing the lactic acid bacteria into groups assignable to altogether 

 dilîerent places in the bacteria system. The biological qualities Will show that 

 certain spherical and rod forms (e. g. streptococci and streptobacteria 

 or betacocci and betabacteria) are at least as nearly related one to an- 

 other as are the s])herical forms or the rod forms respectively among them- 

 selves. The true lactic acid bacteria form altogether a family as natural as could be desired. 

 Buliftliis — ^ like other natural bacteria families — cannot be broken to pieces because it 

 contains species with more or less long, or more or less curved cells, as has hitherto been 

 done in bacteriology, the old generic names, which are purely morphological terms, can 

 likevisc no longer be used without some supplementary prefix, or at any rate not without 

 giving them a new meaning. 



As regards the cultural features of tlie lactic acid bacteria, we can likewise be brief. 

 With the exception of the tetracocci (the acid-forming micrococci and sarcinæ) and cer- 

 tain microbacteria, they thrive best without air, and have therefore, in stab cultures, no 



