ORIGIA T OF LOWEST ORGANISMS. 



on one of Strieker's warm-water chambers placed on 

 the stage of the microscope. Under these conditions, 

 I have seen a Bacterium of moderate size divide into 

 two, and each of these into two others somewhat 

 smaller, in the course of fifteen minutes. 



It is still more worthy of remark, that in all cases 

 (so far as I have been able to observe), this, the most 

 certain sign of vitality which such organisms are 

 capable of manifesting, is shown by those which, 

 from their stillness, might be considered dead. The 

 Bacteria which are about to divide are generally either 

 motionless,* or merely present slight oscillating move- 

 ments. The separation is quickly brought about at 

 the joint, so that the original organism divides into 

 two equal portions ; and these, lying close together, 

 soon develop a new construction as they grow, through 

 which a further division may occur. 



That the Bacteria which reproduce should be in a 

 comparatively -quiescent condition, seems not difficult 

 to understand. Such rudimentary organisms do not ap- 

 pear to possess cilia or other locomotory appendages : 

 their movements are, therefore, in all probability de- 

 pendent upon the mere molecular changes which are 

 taking place within them, and upon which their life 

 .and nutrition depend. The process of fission must, 

 however, be considered as the result of a new effort at 



Those which are quite motionless are always in close 

 apposition either with the under surface of the covering glass, or 

 with the surface of the glass on which they are situated. 



