ORIGIN OF LOWEST ORGANISMS. 47 



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 evaporation could take place from the 

 thin film of fluid, and after one, three, four, or more 

 hours the slide remaining undisturbed most of 

 the particles had subsided, and were found to have 

 come to a state of rest. In order still further to test 

 these views, I took an infusion of turnip, contain- 

 ing a multitude of Bacteria whose movements were 



o 



of the languid description, and divided it into two 

 portions. One of these portions was boiled for about 

 a minute, whilst the other was not interfered with. 

 Then, after the boiled solution had been cooled, a 

 drop was taken from each and placed at some little 

 distance from one another on the same glass slip ; 

 covering-glasses half an inch in diameter were laid 



