32 STUDIES ON FERMENTATION. 



like a moulfl, by absorbing the ox3'geii of the air as it enters 

 the flask. The bulk of the yeast which has been fermenting 

 remains at the bottom of the liquid in the form of an inert 

 deposit. This inertness, however, is apparent rather than 

 real ; the globules may be internally active, without any 

 development of new buds, and the effects of this working may 

 cause them to become more and more languid, and in the course 

 of time may even destroy them. 



The case is quite different when the yeast with which our 

 wort is impregnated, instead of being pure, is mixed to any 

 extent whatsoever with diseased ferments. Should there be 

 any of these in the yeast with which we impregnate our wort, 

 even though their quantity were so infinitesimal that the most 

 skilful observer could scarcely discover them with the microscope, 

 they would multiply in the flask after the beer had been 

 finished, especially if the beer were left for a short time on a 

 stove. In this manner we may secure an excellent test of the 

 original purity of the yeast which we employ in the impregna- 

 tion of our wort. 



Thus it may be seen that the absence of microscopic organ- 

 isms that are foreign to the nature of pure yeast may invariably 

 be noticed in the case of a beer which is sound, and which will 

 remain sound for any length of time, when in contact with pure 

 air, at any temperature. We may see, too, that the presence 

 of these organisms may invariably be detected in an unsound 

 beer, the peculiar unsoundness of which depends upon the 

 peculiar species of the organisms contained in it. It would be 

 difficult to adduce clearer proofs than those which we have 

 given as to the intimate relation existing between these organ- 

 isms and the deterioration of beer. The relation between cause 

 and effect, in the succession of physical phenomena in general, 

 is established by proofs tliat are by no means more decisive. 



