THE BEGINNINGS OF LIFE. 321 



It may naturally be asked if there are any means of 

 deciding whether 'Bacteria^ that have been submitted 

 to a given temperature, and which exhibit movements 

 resembling those known as Brownian, are really dead or 

 living. If the movements are primary, or dependent upon 

 the inherent molecular activity of the organisms them- 

 selves, they ought, it might be argued, to continue when 

 the molecules of the fluid are at rest ; if, on the other 

 hand, they are mere secondary or communicated move- 

 ments, impressed upon the organisms as they would 

 be upon any other similarly minute particles, by the 

 molecular oscillations of the fluid in which they are 

 contained, then the movements ought to grow less, and 

 gradually cease, as the fluid approaches a state of 

 molecular rest if this be attainable. Following out 

 this idea, some months ago, I first tested the correct- 

 ness of the assumption by experimenting with fluids 

 containing various kinds of not-living particles; such 

 as carbon-particles from the flame of a lamp, or freshly 

 precipitated baric sulphate. However perfect may have 

 been the Brownian movements when portions of these 

 fluids were first examined beneath a covering-glass, 

 they always gradually diminished after the specimen 

 had been mounted by surrounding the covering-glass 

 with some cement or varnish. Thus prepared, no eva- 

 poration could take place from the thin film of fluid, 

 and after one, three, four, or more hours the slide re- 

 maining undisturbed most of the particles had sub- 

 sided, and were found to have come to a state of rest. 



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