USE OF INFUSOETA. l77 



that a small bit of deal match-wood, in which 

 a flame has just been extinguished, will burst 

 into a flame again on being immersed in any- 

 one of them. "I myself," the celebrated 

 German chemist last named tells us, " took an 

 opportunity of verifying this remarkable fact, 

 upon finding in a trough of water in my gar- 

 den the fluid coloured green by the presence 

 of various species of infusoria. I filtered it 

 through a very fine sieve, in order to separate 

 all confervse, or vegetable matters ; and then 

 exposed it to the light of the sun in an inverted 

 beaker-glass, completely full, the aperture of 

 which was confined by water. After the lapse 

 of a fortnight, more than thirty cubic inches of 

 gas had collected in the glass, which proved to 

 be very rich in oxygen.'* Here, then, we have 

 actually in these creatures, unsuspected and 

 unseen till the microscope revealed them, a 

 source of pure vital air. From the instant, 

 therefore, that these infusoria appear in stag- 

 nant water impregnated with deleterious mat- 

 ter, that water ceases to act injuriously on the 

 higher orders of plants and animals. To 

 qupte Liebig once more : " In the most exten- 

 sively diffused animalculse, namely, the green 

 and red infusoria, we recognise a most 



