MICROSCOPICAL AND PHYSIOLOGICAL EXAMINATION. 



19 



mash containing ammonium fluoride the yeast is then supposed 

 to continue its vigorous fermentative activity. A necessary 

 condition, without which such a treatment of the yeast cannot 

 produce these results, is that a suitable type of yeast should 

 first be found out by a methodical selection according to 

 HANSEN'S principles. Finally, in this connection, HIRSCHFELD'S 

 observation that acetic acid fermentation can be greatly acceler- 

 ated by adding O'Ol to 0'02 per cent, of hydrochloric acid may 

 also be mentioned. LAFAR'S observations as to the influence of 

 acetic acid on wine-yeasts also furnish examples of such stimu- 

 lating effects. 



All these changes in the nature of the yeast-cells or bacteria 

 are merely transitory. 



5. FLASKS: PASTEUR, CHAMBERLAND, FREUDENREICH, 

 HANSEN, JORGENSEN, CARLSBERO FLASKS, ETC. 



All vessels in which cultures are made must satisfy the 

 condition that they are proof to every contamination from 

 without. Pasteur's flasks satisfy this 

 demand in the highest degree. 1 The 

 illustration (Fig. 3) shows this flask in 

 the improved form employed in the 

 Carlsberg Physiological Laboratory 

 directed by HANSEN. When the 

 hopped wort (preferably filter-bag 

 wort) is boiled, the steam first 

 escapes through the wide straight 

 tube, at the end of which is a 

 piece of india-rubber tubing ; when 

 this is closed (after boiling for about 

 a quarter of an hour) the only outlet 

 for the steam is through the bent 



tube. About ten minutes after, the flask is taken from 

 the sand-bath, and the bent tube may be closed with 



^HEVREUL and HOFFMANN had previously found that when vessels 

 employed in sterilising liquids are provided with open but bent tubes 

 their contents will remain sterile. Although CHEVREUL was thus the 

 first to indicate the principle of these flasks, they will not be mentioned by 

 any other name than that* of PASTEUR, through whom, indeed, they have 

 obtained a wide application. 



FIG. 3. PASTEUR'S Flask. 



