86 MUTUAL RELATION OF BACTERIA. 



grape is the habitat of an abundant flora of fungi, which are intro- 

 duced into the must in the operation of pressing. Of these 

 (exceptional instances apart), the organism exciting alcoholic fer- 

 mentation is the first to develop, because the constitution of the 

 must favours it the most, the result being that the sugar therein 

 contained is split up, and carbon dioxide and alcohol are produced. 

 When this decomposition is effected, the character of the liquid 

 has become changed, and now a new species, exciting acetic fer- 

 mentation, comes into play. This organism was already present 

 in the must, but could not make headway against the predominant 

 yeast, because, in the first place, the alcohol, without which it feeds 

 but indifferently, was lacking. Secondly, even had this substance 

 been present, it could not have been utilised, because of the atmos- 

 phere of carbon dioxide, immediately above the liquid, preventing 

 the free access to the latter of the copious supply of oxygen with- 

 out which the oxidation of the alcohol cannot proceed. Now, 

 however, that both substances are present, the liquid commences 

 to undergo a second alteration, and turns sour, the acetic acid 

 bacteria being now on the surface ; and this condition endures so 

 long as there is any alcohol left. When this is exhausted, a third 

 group of organisms comes to the front, thread fungi establish 

 themselves in the strongly acid liquid and consume the acetic 

 acid, carbon dioxide and water being found. This accomplished, 

 the once again altered nutrient medium is attacked by putrefactive 

 bacteria, which have been carried into the vessel along with the 

 dust in the atmosphere, but can only develop now that the alcohol 

 and acid, which are poisonous to them, are wanting. The liquid 

 is seized upon by these Schizomycetes, and, with their activity, the 

 series of metabiotic phenomena which the wine-must presents to 

 our notice closes. 



The mutual influence of two or more species may be of such a 

 nature that it is impossible for them to live together, the presence 

 of the one species retarding the development of the other. This 

 set of conditions is termed antagonism, a number of examples of 

 which will be given in subsequent sections. 



65. Mixed Cultures. 



When a nutrient medium is inoculated with two or more 

 species of symbiotic organisms, we obtain a mixed culture. Such 

 a culture may, under certain circumstances, yield fermentation pro- 

 ducts that cannot be obtained from any of the component species 

 cultivated singly, but owe their origin partly to the coalescence 

 of the normal products of the individual species, and partly to the 

 reciprocal stimulative action exerted by the associated organisms. 

 A few highly instructive examples of this are given below. 



The first of these which was discovered by NENCKI (I.) is 

 afforded by the bacillus of symptomatic anthrax (Rauschbrand) 



