17 



95 



Table Ild. 





No. of bacteria in 





























Table XXVIII 



• 







3 









4 







5 







"loo 





10 



20 



50 



100 



200 



10 20 



50 100 200 



10 20 



50 



100 



200 



Y -f 



- maltose (as malt extract) ') 



(9,5) 



11,7 



12,2 



13,5 



11,5 



(10,4)12,6 



13,3 16,2 ! 



14,0 



(9,5)' 12,2 



12,6 



18,5 12,6 



Y - 



- dextrose 



6,1 



7,9 



9,2 



6,3 



3,8 



6,5 10,8 10,8 12,0 1 





7,0 13,3 



14,9 



13,1 



8,3 



Y- 



- dextrose covered with 





























parafRn 





9,5 



10,4 



6,3 



5,0 



6,0 13,314,0 13.1 



11,0 



5,4 13,1 



12,2 



11,5 



11,5 



whether we can reckon the strains investigated as belonging to the true lactic 'acid bacteria 

 or not. The fermentation products formed by these bacteria consist as a rule, besides 

 dextro-,lævo-, or inactive lactic acid only of a little succinic acitl and volatile acids (acetic 

 acid with traces of propionic and carbonic acid). Some few species can also form — chiefly 

 from lævulose — a small quantity of mannite and hydrogen. 



As I have already, in several previous works'), described in detail the methods 

 employed for demonstration of the mentioned fermentation products, I shall not go 

 into this again at length. It should merely be noted, that as the acid formed is often a 

 combination of active and inactive acids, the zinc lactates (whose water content and rotary 

 power are used to determine the modification of the lactic acid) should always be allowed 

 to crystallise out in several fractions. The more heavily soluble inactive salts will then ciy- 

 stallise out before the more soluble active ones, and it will thus be possible to form an 

 estimate of their respective values. It should also be mentioned, that mannite may very 

 easily crystallise out from an alcoholic extract of the dessicated culture. If the lævulose 

 has not been entirely fermented, the remains of this should be removed before drying, by 

 boiling with lime milk. .\ decoloration with bone black may then be necessary. Jan 

 S.MiT^), who has worked more particularly with mannite, points out that, where a quanti- 

 tative determination is required after the lime treatment, oxalic acid should be 

 added, and, for removing any possible surplus thereof, again some chalk, as otherwise 

 part of the mannite will unite with the lime. If there should be too little mannite present, 

 to form the crystals easily recognisable under the microscope, then it will be necessary 

 to content oneself with demonstrating it by means of copper sulphate and caustic soda, 

 with which, like other polyvalent alcohols, it gives a dark blue solution^). 



For demonstration of the separate fermentation products, it is of course alwaj-s an 

 advantage to have them in not too weak concentrations; accordingly, the cultures are 

 given at least 4*^/0 sugar and a quantity of chalk sufficient to neutralise all acid formed, 



') In the maltose, however, the grape sugar of the malt extract is included. As the malt extract 

 also contains dextrine, which is to some extent fermented by the bacteria here investigated, it is quite 

 possible to get a greater quantity of acid formed than corresponds to the maltose itself. 



-') I may here refer especially to my "Studien über die flüchtigen Säuren im Käse etc." Centraiblatt 

 f. Bakt. II. Abt. 1904. XIII. 434. 



Zeitschr. f. anal. Chemie 1914. 53. p. 473. 



* To 50 cm' liquid is added 25 cm.' 4X n. Va O// —25 cm.' copper sulphate las with Feuling's 

 liquidi. 



n. K. DViacnskab. Selsk. Skr., iialurvideiisk. og mathein. .\r.l., .s. K;i kke, V. 2. 13 



