94 Lectures on Bacteria. [^ ix. 



rows ; portions of the transverse partition-walls are plainly seen 

 and are indicated by a slight constriction. They have no power 

 of independent movement. In form, therefore, this species resem- 

 bles the Bacterium of vinegar and may be called Micrococcus 

 lacticus, as has been done by van Tieghem. Hueppe, however, 

 states that there is a formation of spores, if I understand him 

 aright, after the endosporous type. If this is confirmed, the 

 Bacterium of lactic acid is a very small Bacillus in our use of 

 the term, and must be so named. 



It is evident that this Micrococcus or Bacillus is always 

 present in milk, not of course when it comes from the udder, 

 but as soon as it is in use. The germs of the organism are 

 diffused to such an extent in the cattle-stalls and in the vessels 

 of the dairy that it never fails to be developed. This is why 

 milk turns sour, because the Bacterium excites lactic acid- 

 fermentation of the sugar contained in the milk ; and when 

 the acidification has reached a certain point, the lactic acid 

 causes the homogeneous gelatinous coagulation of the casein, 

 which is characteristic of good buttermilk. 



Further physiological peculiarities of this Bacterium have been 

 described in detail in Hueppe's careful treatise, and should be 

 studied there. 



In the Bacillus or Micrococcus lacticus which has now been 

 described we have made acquaintance with a very widely diffused 

 and active lactic acid-ferment, but it is by no means the only 

 one. On the contrary, the number of species of Bacteria which 

 form lactic acid in saccharine solutions or in milk appears to 

 be more than usually large. Hueppe alone mentions five, and 

 all Micrococci ; one of these is known to us as M. prodigiosus of 

 the blood-portent mentioned on page 14. Two others Hueppe 

 discovered to be the exciting cause of the lactic acid which 

 occurs in the human mouth, while he found the Bacillus first 

 described only occasionally in the mouth. We still wait for 

 closer investigation into most of these forms, and into their 

 operation as ferments. It is, however, already plain that on all, 



