30 STUDIES ON FERMENTATION. 



diately issue through the bent tube. On permitting the flask to 

 cool, it will then be ready for impregnation. If there were any 

 fear that some foreign germ of an unknown nature might have 

 effected an entrance during cooling, or had not been destroyed by 

 the steam (which is always a little super-heated, in consequence 

 of the resistance which it meets in escaping), we need only 

 place the flasks on a warm stove, and leave them there for a few 

 days or a few weeks to ascertain whether the liquid in them 

 has undergone any change. We should then only use those 

 flasks which contain a sound liquid. 



At the same time we must warn our readers that this cause of 

 error does not exist once in a thousand times, especiall)^ if we use 

 an asbestos stopper to prevent the entrance of little insects which 

 are attracted by the odour of the liquid, and which instinctively 

 seek to enter at the extremity of the tube, and to pass through 

 it into the flask. In going so far, and incurring such labour in 

 search of their food, they condemn themselves to certain death, 

 for they are sure to be drowned, since it would require an 

 intelligence superior to that which they possess to enable them 

 to get out of the flask ; the liquid, morever, could not fail to 

 undergo some change, in consequence of the particles of dust 

 that the insects would introduce into it. 



After having passed the flame of a spirit-lamp quickly over 

 the india-rubber tube, the glass stopper, the curved tube, and 

 even over the fingers of the operator, we mav withdraw the 

 glass stopper, and introduce the pure yeast by means of a glass 

 pipette that has been previously heated. This yeast is kept in a 

 vessel also free from the dust floating in the air. However few 

 globules of yeast tlie glass tube may take up, it is sure to 

 introduce a hundred or a thousand times more than is necessary 

 for the impregnation of the liquid. The glass stopper must then 

 be replaced immediately, after having been again quickly passed 

 through the flame. In transferring our yeast from the vessel 

 containing it to the flask, by means of a glass pipette, it is 

 exposed to another cause of impurity, since we cannot avoid 

 bringing it in contact with the common air. If this risk 



