FERMENTATION. IO5 



so that in fermenting tanks in which, of course, large quantities 

 of carbonic acid gas accumulate the films are not usually met 

 with. From this one may gather how laboratory experiments 

 may go wrong, or give untranslatable results, when the exact 

 conditions met with in nature, or on a large scale, are not 

 adhered to ; it also explains the different results that 

 have been obtained by various workers, the conditions in 

 their experiments not always being the same. For instance, 

 in Chamberland or ordinary flasks covered with filter paper 

 the film forms will develop rapidly as soon as the primary 

 fermentation is completed ; whilst in the closed Pasteur 

 flasks, in which the air cannot be changed rapidly, the 

 films grow comparatively slowly. 



To produce these films Hansen proceeded as follows : 

 Having obtained his pure cultivations, drop cultures were 

 made into car.efully sterilized four-ounce flasks, half filled with 

 sterilized wort and protected from falling particles by being 

 covered with sterilized filter paper. As soon as the films be- 

 came apparent to the naked eye they were examined. They 

 appear, according to Hansen, as small opaque points, which 

 gradually increase in size and then run together, forming 

 irregular patches floating on the upper surface, with a con- 

 vexity on the side resting on the fluid. The film at length 

 overspreads the whole surface and becomes adherent to the 

 wall of the flask at the margins ; on shaking the flasks much 

 of the film can be made to sink, but a new one forms to fill 

 up the gaps that are left. 



These young films he divided into two groups, the first 

 consisting of Sacch. cerevisiae, Sacch. Pastorianus II., Sacch. 

 ellipsoideus II., in none of which could he find mycelium-like 

 colonies (at one time it seemed that Hansen's researches had 

 demonstrated this fact) ; whilst in the second group, which 

 included Sacch. Pastorianus I. and III. and Sacch. ellipsoideus 

 I., such mycelial colonies were early developed. Later 

 researches have tended to show that this division is very 

 much a matter of time, and that it cannot now be looked 

 upon as having any real scientific value. 



As regards the temperature at which these films are 

 developed Sacch. cerevisiae and Sacch. ellipsoideus I. are 

 developed between 38 and 6 C., the three Pastorianus 

 varieties between 34 and 3 C. ; Sacch. ellipsoideus II., 38 

 to 40 C., and 3 C. The film of this latter appears to be the 



