284 



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 fer- 

 ments, 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 iodium, all belonging to the species 

 Gramdobacter saecharobutyricitm. 



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 in the milk, the fermentations of Aerobacter 

 and the lactid 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. 



i . 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, Lactobacillus and Lactosanina, of which the 

 two first only occur in the dairy products 1 ). 



They are always immotile, no-spore forming bacteria, which bear drying 

 very well and which, by heating to 65 or 75 C., in which they just remain alive, 

 while these temperatures are deadly ao most other non sporeproducers, may be 

 separated from these (lacticisation). They require for nitrogenfood peptones, 

 such as are found in milk, malt extract, or other juices of plant- or animal 

 origin, and for carbon food certain sugars, which may differ for different species. 

 They do not peptonise proteids and, thus, do not liquefy gelatine; the secreted 

 lactic acid can dissolve a certain quantity of caseine, but chemically this sub- 

 stance remains unchanged. These circumstances regulate their distribution in 



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

 species of Lactosarcina. When Emm er ling asserts to have found a yellow Sarcina 

 in Armenian mazun (Centralbl. f. Bacteriologie, 2te Abt. Bd. 4, p. 418, 1898), this can 

 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. 



