285 



nature, where they are by no means general, but may rapidly, multiply, especi- 

 ally under the influence of man. They are, however, found in the soil and can, 

 by methods mentioned below, be accumulated and cultivated in a condition of 

 pureness. 



They are always more or less distinctly microaerophilous, some species or 

 varieties can, however, grow very well at the air; other forms cannot and be- 

 have as real anaerobics. Access or absence of air is commonly of no consequence 

 to the acid formation, but in the yeast industry a species is used, which at full 

 atmospheric pressure produces no acid, and in the dairy industry are also forms 

 which display the same property. 



Always, even on good nutrient media, to which belong in particular malt- 

 extract agar, and milk- or whey-agar, the growth of the colonies remains li- 

 mited, especially if the air and the produced acid can act simultaneously. If the 

 acid is neutralised by chalk the growth of the colonies at the air may also be- 

 come important. Yet, in most cases, the recognition of these ferments may repose 

 on the smallness of their colonies compared with those of other bacteria. 



Catalase is constantly absent, and hereupon an excellent diagnosis can be 

 based, for which it is only necessary that a culture plate, on wich all kinds of 

 bacteria may occur, be flowed with strongly diluted hydrogensuperoxyd which 

 is by all microbic species, except the lactic acid ferments, indifferently whether 

 they belong to Lactococcus, Lactobacillus or Lactosardna, changed into a scum of 

 little oxygen bubbles. 



Even the lately described *) large celled Sarcina, which in consequence of 

 continued research I now consider as identic with the stomach sarcine (Sardna 

 ventriculi), and whose acid producing power is very slight, - i. e. 3 c.c. of normal 

 acid per 100 c.c. of maltextract or glucose broth, --does not at all decompose 

 hydrogen superoxyd. 



If we consider how generally catalase is met with in the animal and ve- 

 getable kingdom, as also in the microbes, its very absence in the lactic ferments 

 appears in a peculiar light. 



All active lactic acid ferments from milk invert sugar (invertase reaction) 

 and can more or less easily decompose esculine and indican (emulsine reaction). 

 The reaction on esculine is demonstrated by introducing, for example, o,i/o of 

 this substance and a fews drops of ferricitrate solution into whey agar or whey 

 gelatin. Streaks drawn on it of species which decompose esculine produce inten- 

 sely brown or black diffusion fields of esculetiniron, brown at more alcaline, black 

 at more acid reaction, so that the lactic acid ferments become recognisable by 

 the black fields in the midst of which their colonies are placed ~). So long as 

 esculine is present it is recognised by the magnificent blue fluorescence of the 

 whole plate at feeble alcaline reaction. Indican may be used in a corresponding 

 way but then no iron salt is wanted as the indoxyl produced from the glucosid 

 oxidises of itself at the air to indigo blue. The lactic acid ferments decompose 



J ) These Proceedings 25 February 1905. Archives Neerlandaises T. i and 2. T. 11, 

 p. 200, 1906. 



2 ) The knowledge of this extremely sensitive reaction, which has been applied for 

 years in my laboratory, I owe to my colleague Mr. H. Ter Meulen. 



