552 THE NATURAL HISTORY OF 



them merely to pass into the still form, in which they 

 retain their vitality for years. 



Cohn observed very frequently that the contact of 

 metal with the water in vs^hich the Profococcus-cells were, 

 was destructive to their life. 



In the still form, the phenomena attendant upon the 

 cessation of life, are somewhat different from those in 

 the motile cells. In certain circumstances, the con- 

 tents, particularly in the red zoospores, dissolve, from 

 the periphery, into innumerable minute droplets. Or a 

 peculiar dissolution of the coloured contents takes place, 

 in such a way that they lose their colour, also from without 

 to within, so that at last the cell appears dense and 

 opaque, but altogether colourless, and is deprived of all 

 vitahty. (Pig. 43.) 



The paper then concludes with some general consider- 

 ations. 



1. The question arises, whether the Protococcus is 

 necessarily to be regarded in all its stages of development 

 as a Plant ; or whether it should not rather be referred 

 to the Animal kingdom. 



To any one who reads the writings of the most distin- 

 guished observers on this subject, it appears almost in- 

 comprehensible, that any doubt could exist whether any 

 organism, when sufficiently investigated, should be an 

 animal or a plant. Por all, nearly without an exception, 

 agree in this, that an animal and a plant are essentially 

 and typically of distinct structure, and that this essential 

 diversity must also be expressed in the most minute 

 and lowest organisms ; and that, therefore, there can be 

 no question of any real analogy between an animal and 

 a plant, to say nothing of a relationship or a transition 

 from one into the other. 



It appears, however, to Cohn, that the question of 

 animal or plant has been stated too generally, and 

 requires to be defined with greater precision. As the 

 question is generally put, it would include the inquiry 



