9 



87 



b. Methods of Investigation. 



In order to identify a micro-organism, the following points must be determined: 

 1. Its morphological and cultural features. 

 II. What sources of energy and nutritive matters it can utilise. 



III. Its manner of utilising the same. 



IV. Its attitude toward diiïerent temperatures. 



V. Its agglutination and other possil)le specific qualities. 



I. ^^lorpholoKical and Cultural Features. 



Of the three principal morphological qualities of bacteria: the arrangement of the 

 flagella, the shape of the cell, and the spore formation, the arrangement of the flagella 

 is, as I have shown in „Hovedlinierne i det naturlige Bakteriesystem", of primary impor- 

 tance^). The shape of the cell, on the other hand, is merely a generic character, and we 

 may, within one and the same family, encounter sphere, rod and screw forms, a» is 

 well known in the case of the red sulphur bacteria, and as we shall also find from an 

 example among the lactic acid bacteria. As all these bacteria appear immotile, and do not 

 form spores, we have, in reality, no morphological indication whatever to go upon when 

 placing them in the bacteria system. On the other hand, their biological qualities are so 

 pronounced, inasmuch as they require just as complicated nourishment as animals, that 

 there can be no doubt as to their place, viz. among the order of Peritrichinæ. 



A very important distinctive feature in lactic acid bacteria, and 

 one which separates them sharply from the coli and aerogenes bacteria isthat they are 

 Gram positive. The first reaction therefore, to which we had recourse with the isolated 

 acid formers was always to ascertain their behaviour in respect of the Gram staining 

 process. Casein being Gram negative, the Gram staining method is excellently adapted 

 to milk preparations. More frequently, however, the simpler staining with methylene 

 blue is employed. This method is likewise used for demonstrating the presence of volutin 

 grains which are frequently met with in several of the rod-shaped lactic acid bacteria. 

 The grains are thereby stained dark blue as a rule, but at times also red. Fuchsin is not 

 suitable for milk preparations, as it colours the casein as strongly as the bacteria. In demon- 

 strating the formation of capsules in milk, however, this is an advantage in itself, as the 

 unstained capsule then appears very distincly, and we have thus succeeded in showing 

 that all lactic acid bacteria form capsules at their first stage of develop- 

 ment. In some few strains, this capsule can attain very considerable 

 size, but in most, it soon disappears without preliminary swelling or 

 slime formation. The faculty of forming slime in milk is more frequent 

 in some species than in others, but it is highly variable, and therefore 

 absolutely inapplicable as a species character. 



M Die Hauptlinien des natürlichen Bakteriensystems. Centralblatt f. Bakt. II. Abt. 1909. X.XII. 

 No. 11 — 13. In this work it is pointed out that on the other hand the mere fact of a bacteria possessing 

 flagella or not is of no systematic importance, and we also find closely related species las for instance 

 hay and anthrax bacille, coll and aerogenes bacterial of which one is motile and the other immotile. 



I). K. D. Vidensk. Selsk. Skr., iinturv Ulensk. i>g nialheni Afd.. 8 Hække. V. ; 12 



