( 18 ) 



lasting some hours, is replaced by a butyric acid fermentation which 

 again, after some time is succeeded by a lactic acid fermentation. 

 Externally the Aërobacter and the butyric acid fermentations cannot 

 be distinguished, bui this can be dune easily with the microscope. 



If 3 to 5 % chalk is added to a culture in a stoppered bottle at 

 35° to 40° C, the butyric acid fermentation can go on longer, and 

 by early transplanting, likewise in milk with chalk and with exclusion 

 of air, check the development of lactic acid ferments, without, 

 however, quite dispelling them. 



Microscopically the butyric acid fermentation may be recognised 

 by the long, thin, at neutral reaction highly motile rods, sometimes 

 mixed with elongated or more rounded Clostridia, colouring blue by 

 iodiuin, all belonging to the species Granulobacter saccliarobutyricuvi. 



To ' accumulate from such a crude butyric acid fermentation in 

 milk the lactic acid ferments, which hardly ever lack there, it will 

 suffice to transplant some drops into milk without chalk, and, if 

 necessary, to repeat this after the butyric acid fermentation, which 

 always sets in at first, is finished. Whether this be done in open or 

 closed bottles or tubes, at 37" to 40° C, lactic acid rods of the genus 

 Lactobacillus will be seen to appear, which by repeated transplantations 

 completely dispel the butyric acid ferments. 



If in these experiments instead of using fresh, unheated infection 

 material, the soil, water, or faeces are previously heated to 80° or 95°C, 

 by which only spore-forming microbes can develop iu the milk, the 

 fermentations of Aërobacter and the lactic acid ferments do not arise, 

 their germs producing no spores, but a butyric acid fermentation is 

 obtained, from which the aerobic spore-formers may be dispelled by 

 repeated transplantation at exclusion of air. 



1. Properties of the active lactic acid ferments. 



As many bacteria of the most different groups can produce lactic 

 acid it seems not superfluous to indicate what are the characteristics 

 of the lactic acid ferments proper. 



The active forms of dairy industries, yeast manufactories, distilleries, 

 tanneries, and breweries, although joined by transitions, may be 

 practically classified into the physiological genera Lactococcus, Lacto- 

 bacillus and Lactosarcina, of which the two first only occur in the 

 dairy products 1 ). 



!) In the chief floras of milk- and dairy products occur, to my knowledge, no 

 species of Lactosarcina. When Emmerling asserts to have found a yellow Sarcina 

 in Armenian mazun (Centralbl. f. Bacteriologie, 2t- Abt. Bd. 4, p. 418, 1898), 

 this can only have been a common infection from without. Also in butter sarcine 

 species may accidentally occur but they do not belong to the chief flora, which 

 consists of lactic acid ferments and lipophili. 



