STUDIES OX FERMEXTATIOX. 295 



a thing were possible, between the mercury and the sides of 

 the delivery-tube was altogether prevented, since the bacteria 

 would consume every trace of oxygen which might be dissolved 

 in the liquid lying on the surface of the mercur}^ Hence it 

 is impossible to imagine that the slightest trace of oxygen 

 could have got into the liquid in the flask. 



Before passing on we may remark that in this ready 

 absorption of oxygen by bacteria we have a means of de- 

 priving fermentable liquids of every trace of that gas 

 with a facilit}'^ and success equal or even greater than by the 

 method of preliminary boiling. Such a solution as we have 

 described, if kept at summer heat, without any previous boiling, 

 becomes turbid in the course of twenty-four hours from a 

 spontaneous development of bacteria ; and it is easy to prove 

 that they absorb all the oxygen held in solution.* If we 

 completely till a flask of a few litres capacity (about a gallon) 

 (Fig. 67) with the liquid described, taking care to have the 

 delivery-tube also filled, and its opening plunged under 

 mercury, and, forty-eight hours afterwards, by means of 

 a chloride of calcium bath, expel from the liquid on the 

 surface of the mercur}^ all the gas which it holds in solution, 

 this gas, when analyzed, w'ill be found to be composed of a 

 mixture of nitrogen and carbonic acid gas, without the least 

 trace of oxygen. Here, then, we have an excellent means of 

 depriving the fermentable liquid of air ; we have simpl}' to 



peculiarly adapted to the propagation of these organisms, which it would 

 be well to compare for its utility in studies of this kind with our solution 

 of lactate and phosphates. The following is Cohn's formula : — 

 Distilled water . . . . . . 20 c.c. (0'7 fl. oz.) 



Phosphate of potassium 

 Sulphate of magnesium 

 Tribasic phosphate of lime 

 Tartrate of ammonia 



O'l gramme (1'5 grains). 



0-1 



0-01 ,, (0-15 grain). 



0-2 ,, (3 grains). 



This liquid, the author says, has a feeble acid reaction and forms a per- 

 fectly clear solution. 



* On the rapid absorption of oxygen by bacteria, see also our Memoire 

 of 1872, sur les Generations dites Spontanees, especially the note on page 7S. 



