220 ROPINESS IN MILK, WINE, BEER, ETC. 



shaped, 0.8 p. broad, 1.6-2.4 M l n g> ana " mostly single, though not infrequently 

 joined in pairs. 



In their behaviour towards beer-wort, however, they differ in a notable 

 manner. It is true that both of them produce ropiness, but not of the same 

 type. If B. v. I. is in action, then, in proportion as the viscidity of the liquid 

 increases, a number of mucinous, yellowish-white patches, terminating below in 

 branches, appear on the surface. In this way a coating of mucus is formed, the 

 surface of which is gradually covered with protuberances produced by bubbles of 

 the carbon dioxide liberated during this fermentation. With B. v. II., on the 

 contrary, this coating is absent ; moreover, the evolution of carbon dioxide is less 

 copious, and the ultimate degree of ropiness less pronounced than in the first 

 case. Whilst the malady is in progress, the colour of the wort changes to a 

 chicory-brown, and at the same time an odour develops, which cannot be more 

 closely defined, but which of itself suffices to reveal the presence of the com- 

 plaint. A further characteristic affording a means of distinguishing between 

 these two species of bacteria is their behaviour towards a sterilised solution of 

 3 grams of cane-sugar and i gram of peptone in 100 c.c. of water. This medium 

 is made viscid and ropy by B. v. I. alone, the second species producing nothing 

 more than a persistent turbidity, accompanied by the evolution of carbon dioxide. 

 Milk is altered by both species in the same manner as wort. 



The fact that both these organisms also cause ropiness in nutrient solutions, 

 devoid of sugar and containing no organic matter beyond calcium lactate or 

 ammonium tartrate, is also interesting. As a matter of fact, a high content of 

 sugar is even injurious to the organisms. This discovery agrees with the ex- 

 perience gained in practice, that beers with a low attenuation (and therefore a 

 higher sugar-content) are comparatively seldom ropy. The proximate cause of 

 this alteration of the medium is a mucus excreted by the bacteria. In the 

 presence of sugar, carbon dioxide is liberated, arid presumably a small quantity 

 of another acid is also formed, since the acidity increases with the ropiness. 

 The mucus is not a uniform substance, but consists of at least two constituents, 

 one of which (insoluble in water) is characterised by its content of nitrogen. 

 This fact harmonises with the circumstance that the malady sets in earlier in 

 proportion as the nitrogen-content of the nutrient medium is greater. It also 

 explains the fact, noticed in practice, that worfcs rich in protein, peptones, and 

 the like, are those most readily becoming ropy. A higher content of acid (0.15 

 per cent, reckoned as lactic acid) restricts the development of both these species 

 of fission fungus ; but alcohol, even in the proportion of 6 per cent, by volume, 

 is powerless to injure them. In both cases growth proceeds at all temperatures 

 between 7 and 42 C., and is most vigorous at about 33 C. 



A third viscous ferment, also discovered by Van Laer, differs from the other 

 two in its property of liquefying gelatinised meat- juice. 



L. YANDAM (I.) obtained from ropy English beer pure cultures of a fourth 

 organism (Bacillus viscosus III.) in the form of rods 0.7 p. broad and 1.3-2.0 /u 

 long, mostly isolated, but frequently also forming bands of two or three cells. 

 So far as can be gathered from the particulars given, ropiness is produced, not 

 by any metabolic product excreted by the bacillus, but by the thickened cell 

 membrane of the organism. In other ways, too, this microbe differs from Van 

 Laer's bacilli. For instance, the development of the organism and the gelatini- 

 sation of the medium occur only in presence of sugar, and the degree of ropiness 

 is proportional to the amount of sugar eliminated. No evolution of gas could be 

 detected in wort cultures. The unrestricted access of air is essentially necessary 

 to the growth and activity of this bacillus. The organism is incapable of injuring 

 beer except when present in large numbers in the wort before the commencement 

 of primary fermentation. 



