EELATIONS OF BACTERIA AMONG THEMSELVES 43 



The state of matters in which two or more organisms work hand in 

 hand, each helping the other, is called Symbiosis. Other examples of 

 sj'mbiosis are the association of Streptococcns and the bacillus causing 

 diphtheria, Bacillus coli and yeasts, the bacillus causing lock-jaw and 

 putrefactive bacteria, and the association between Diplococcus pueu- 

 moniae and Proteus vulgaris. This subject is very little understood, 

 but its importance cannot be overestimated, especially the conditions 

 of symbiosis of the pathogenic bacteria with other organisms. Thus it 

 does not follow that because a certain pathogenic microbe is present in 

 our bodies, we suffer from the disease in question. We suffer only if 

 this microbe multiplies, and multiplication takes place only if certain 

 conditions hold. It is important that we should know more of the 

 organisms which tend to bring about these conditions. The Caucasian 

 drink called Kephir is an interesting result of symbiosis. This is ar 

 effervescent, alcoholic sour milk prepared from the milk of sheep, 

 goats, and cows. The method of its manufacture is simple. A few 

 "kephir grains" are added to the milk, which is then allowed to 

 stand for 24 hours at room temperature, then poured off to allow 

 fresh milk to be added to the grains. Fermentation is complete 

 in two or three days, the mixture containing about two per cent, of 

 alcohol. The "kephir grains" are a mixture of three organisms, s 

 filamentous bacillus forming " zoogloea," a lactic-acid producing bacillus, 

 and a yeast. These three organisms are obviously in a state of sym- 

 biosis, though what the exact nature of it is, is very difficult to say. 



Another well-known instance is the so-called ginger-beer "plant," 

 which is the agent in the production of stone ginger-beer. These 

 " plants " consist of two organisms, a yeast called Saccharomyces 

 pyriforme, and a bacillus called Bacterium vermiforme. The production 

 of ginger-beer will be described in a later section, it is sufficient here to 

 notice the symbiosis of the two organisms. Another interesting case is 

 that of the two yeasts, Saccharomyces pastorianus III,, and Saccharo- 

 myces ellipsoidens II., which, according to E. Chr. Hansen, acting 

 together, cause turbidities and other beer diseases, though each alone 

 is harmless.! 



^ The importance of a, knowledge of symbiosis, especially to the practical man, 

 is seen by the results of Nenoki's experiments. The bacillus of symptomatic 

 anthrax in nutrient solutions containing cane-sugar, produces the following sub- 

 stances as fermentation products : hydrogen, carbon-dioxide, normal butyric acid, 

 and active lactic acid. On the other hand, micrococcus aeidi paralactici in the 

 same medium produces almost exclusively optically active paralaotic acid. Now, 

 when cultivated together in the same nutrient solution, in addition to the above- 

 mentioned substances, normal butyl-alcohol is produced. 



