1900.] on Symbiosis and Symbiotic Fermentation. 271 



times of great length and much convoluted. This sheath is normally 

 formed by the microbe, and the process can sometimes be watched. 

 The bacterium sometimes partially escapes from the end as it is 

 beginning to form it, and so the sheath continually elongates ; the 

 part behind the organism remaining empty. The conjoint organism 

 can be synthesised from pure cultures of the two symbionts, but it is 

 not very easy to make them come together, as the existence of the 

 complete structure is dependent on the activity of them both. 



The most efficient method is to prepare a glass vessel containing 

 an appropriate nutrient fluid, and to suspend inside it another vessel 

 of porous porcelain, so that the walls of the two do not come into 

 contact. This porcelain pot must contain the same nutritive solution. 

 The yeast must then be sown in the inner vessel and the bacterium in 

 the outer one. In this condition the two organisms cannot come into 

 contact, but the products of their activity can mis by diffusion through 

 the porcelain vessel. The whole apparatus must then be kept im- 

 mersed in an atmosphere of carbon-dioxide, so that no oxygen may 

 gain access to the microbes. After a time, when both are growing 

 vigorously, a little of the yeast must be transferred to the outer vessel, 

 when the two will grow together into the conjoint form. 



Another method, which does not, how r ever, give such satisfactory 

 results, is to prepare a good growth of the yeast in a culture-fluid 

 containing bouillon and grape-sugar, and while its activity is at its 

 height to inoculate the culture with some of the bacteria. 



In the condition of symbiosis both members are more active than 

 when they exist separately. The cells of the yeast bud more actively 

 and the coils of the bacterium are formed more freely. More carbon- 

 dioxide is evolved from the fermenting liquid. The details of the fer- 

 mentation have not yet been examined, but certain points of interest 

 as to the inter-action of the one with the other have been established. 



The sheathing form of the bacterium can only be produced when 

 oxygen is replaced by carbon-dioxide. The advantages of the pro- 

 tective sheath to the microbe seem apparent. In the symbiotic 

 association the yeast absorbs the oxygen, and during its fermentative 

 activity produces carbon-dioxide, thus providing the necessary con- 

 ditions for the formation of the sheaths, that is, for the full develop- 

 ment of the bacterium. When they are cultivated separately, the 

 yeast appears to form some substance or substances which inhibit the 

 formation of the sheaths. This does not occur when the symbiosis 

 is established. It may be connected perhaps with the relative 

 quantity of the two organisms present together in the free condition, 

 or with some variation of the vital processes under the different 

 conditions of cultivation, but the cause is at present obscure. The 

 bacterium benefits by extractives or other substances excreted by 

 the yeast, and the latter profits by the removal of these matters 

 through the agency of the former. 



A third organism which must be classed with both these occurs in 

 Madagascar as a curious gelatinous-looking substance found attacking 



