48 ORIGIN OF LOWEST ORGANISMS. 



on, and the superfluous fluid beneath each was re- 

 moved by a piece of blotting-paper. When only 

 the thinnest film of fluid was left, the covering- 

 glasses were surrounded by a thick, quickly-drying 

 cement.* Examined with the microscope immediately 

 afterwards, it was generally found that the Bacteria 

 which had been boiled presented a shrunken and 

 shrivelled aspect whilst some of them were more 

 or less disintegrated though, as far as movement 

 was concerned, there was little to distinguish that 

 which they manifested, from that of their plumper- 

 lookincr relatives which had not been boiled. 



o 



If the specimens were examined again after twenty- 

 four or more hours, there was still very little difference 

 perceptible between them, as regards their move- 

 ments. And the same was the case when the spe- 

 cimens were examined after a lapse of some days or 

 weeks. One important difference does, however, soon 

 become obvious. The Bacteria which have not been 

 boiled, undergo a most unmistakeable increase within 

 their imprisoned habitat ; whilst those which have been 

 boiled, do not increase. The two films may be almost 

 colourless at first (if the Bacteria are not very abundant), 

 but after a few days, that composed of unboiled fluid 

 begins to show an obvious and increasing cloudiness, 



* I always employ a solution of gum mastic and bismuth in 

 chloroform. If a different varnish be employed, it is of course 

 necessary to ascertain whether its application is injurious to the 

 enclosed Bacteria. 



