286 



these two glucosides, slowly indeed, yet these reactions are very characteristic 

 and useful. Amygdaline is not decomposed by the lactic acid ferments 1 ). 



To the most remarkable properties of the lactic acid ferments belongs their 

 power of reducing levulose to mannite 2 ), which latter substance may even in 

 concentrated nutrient solutions be recognised by its ready cristallisation at 

 evaporation. A single drop dried on the object glass, commonly gives at micro- 

 scopical investigation full certainty as to the existence of this reaction. 



The lactic acid ferments thereby strongly contrast with the so nearly allied 

 vinegar bacteria, in as much as the latter do just the reverse, i. e. they change 

 by oxidation mannite into levulose. 



Like so many other bacteria the lactic acid ferments possess, also with 

 regard to various pigments, a strongly reducing power, as is easily shown by 

 inoculation into deep test-tubes of boiled milk coloured with litmus. The red 

 litmus is first in the depth, later till near the surface quite discoloured, to turn 

 red again by shaking with air. The thickness of the red layer in the curdled 

 milk admits an accurate measure of the intensity of the growth and of the 

 reduction process. The thinner the red layer the more intensive both functions 

 must be. 



2. Factors of variability. 



Many, perhaps all lactic acid ferments display a high degree of variability 

 as well in physiological as in morphological properties. Nevertheless this varia- 

 bility in different stocks, coming from different isolations of the same species, is 

 not always equal by far, which may give rise to trouble in the study of the 

 specific properties. The circumstances causing the variability are but partly known; 

 decidedly belongs to them an oxygen pressure, too far above or too far beneath 

 the optimum for the vital functions, which may, especially for the bacterium of 

 the long whey (Lactococcus hollandiae) , be demonstrated with exceeding clearness. 



This remarkable species is characterised by a vigorous slime formation when 

 cultivated in milk or whey, but loses this power at temperatures above 20 C., 

 as well at the ordinary pressure of the atmospheric oxygen, as at complete ex- 

 clusion of it, if the changed influence is allowed to act during some time on 

 the growing microbes. This is shown by cultivating the whey in a closed bottle; 

 the upper layer, just beneath the stopper, where a little air can find access, be- 

 comes quite liquid and contains a hereditarily constant, common Lactocoecus, for- 

 ming little acid and no slime. Also by cultivating the long whey microbe in 

 tubes of boiled milk with access of air, after one or two re-inoculations, a Lacto- 



') Amygdalin is decomposed with much more difficulty by the action of microbes 

 in general than the other glucosides named in the text. Moulds mostly decompose it 

 into amygdalinate of ammonium; beer yeast into amygdalonitril glucosid and glucose. 

 Splitting under production of bitter almond oil, hydrocyanic acid and glucose I detected 

 hitherto only with Saccharomyces apiculatus and with the anaerobic ferment of butyric 

 acid fermentation, Granulobacter saccharobutyricum. 



2 ) Ferments lactiques de 1'industrie. Archives Neerlandaises 1901. Kayser, Fer- 

 mentation lactique. Annales de 1'Institut agronomique 1904. 



