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ditions for lactic acid formation by the active ferments are wanting or must at 

 least be very unfavourable there. 



As to the first point I refer to the following experiments. 



If sterile milk is infected with faeces of different origin (man, cattle) and 

 treated as described for the elective culture of Lacfococcus, without access of air 

 and repeatedly re-inoculated at a temperature between 23 to 26 C., the said 

 genus of microbes is indeed obtained by which as good cream souring can be 

 obtained as with the pure cultures prepared in the before described way. 



If sterile milk is infected in a corresponding way and exposed to the con- 

 ditions wanted for Lactobacillus, that is, if cultivated in absence of air at 40 to 

 45 C., a fermentation of coli will first arise and later or simultaneously a butyric 

 acid and no lactic acid fermentation, which latter would inevitably arise if the 

 lactic acid ferments were present in a rather considerable number. Only by repeated 

 transferences Lactobacillus is produced, which after some inoculations forms 10 to 

 13 c. c. of normal acid. 



Hence, there is no doubt as to the presence of Lactobacillus and Lactococcus 

 in normal faeces. They are, however rare, and belong by no means to the intestinal 

 flora proper, like coli, but to the accidental flora, which consists of all that is 

 introduced and is able to pass the stomach and intestines alive, without multi. 

 plying. There seems to be no cause to attribute any important influence to 

 this fact. 



As to the second point, why in the intestinal canal the conditions for the 

 growth of the active lactic acid ferments are wanting, it is that in the contents 

 of the intestines an alcalic reaction exists, and that the sugars which are formed 

 or introduced there, in as much as they are not absorbed by the intestinal wall, 

 will surely be attacked by coli, which in these circumstances is the stronger and 

 dispels all competitors. 



Why coli (and acrogenes) so completely defeat the lactic acid ferments, should, 

 to my opinion, be explained by the important fact, not sufficiently considered in 

 literature, that the first mentioned species can quite well live on peptone only, 

 and multiply at its expense, while the active lactic ferments completely lack this 

 faculty and, beside peptone, require a carbonhydrate for food. 



If, moreover, it is borne in mind that coli in the presence of a carbonhydrate 

 can also feed on other sources of nitrogen than peptone, for example on amines 

 and ammonium salts, whereas the active lactic acid ferments cannot, and deci- 

 dedly want peptones for nitrogen food, it is clear that for the different forms 

 of coli practically every where in the intestinal contents a good feeding material 

 is present, and that in the few localities where it would also be sufficient for 

 the lactic acid ferments, it will be seized upon by coli. Where only peptones occur, 

 coli will moreover increase the already alcalic reaction of the contents and thus, 

 not for itself but for the lactic acid ferments, render the conditions of life more 

 unfavourable. 



Hence it seems evident why in the intestinal canal a coliflora can exist but 

 no lactic acid flora. 



The yellow coloured faeces of babies during the lactation period may be 

 alleged to support this view. They consist microscopically almost solely of bacteria. 



