330 FRAGMENTS OF SCIENCL 



the six tubes in succession by means of the pipette. Per 

 mitted to remain without further precaution, every one 

 of the tubes would putrefy and fill itself with life. The 

 liquid has been in contact with the dust- laden air outside 

 by which it has been infected, and the infection must be 



destroyed. This is done by plunging the six tubes into 

 a bath of heated oil and boiling the infusion. The time 

 requisite to destroy the infection depends wholly upon 

 its nature. Two minutes' boiling suffices to destroy some 

 contagia, whereas two hundred minutes' boiling fails to 



