THE BIOLOGY OF DAILY LIFE. 71 



and that in many cases it is a mere matter of 

 convention, whether we call a given organism 

 an animal or a plant" (p. 128). 

 He then cites the case of a living body common in 

 one form in tan-pits, and called ^ihalium septicum, and 

 which, by a kind of biological allotropism (possibly ana- 

 logous to chemical allotropism or power of appearing in 

 two or more forms, while, like Proteus, retaining iden- 

 tity), is sometimes like a plant and sometimes like an 

 animal in its way of feeding, or "mode of assimilation.' 7 

 By a curious inversion of the rule of proceeding 

 from the well-known to less known he argues from 

 the imperfectly and badly known, to the utter over- 

 throw (philosophically) of one of Nature's most im- 

 portant distinctions. 



" Is this a plant, or is it an animal ? Is it both 

 or is it neither ? Some decide in favour of the 

 last supposition, and establish an intermediate 

 kingdom, a sort of biological No Man's Land 

 for all these questionable forms. But as it is 

 admittedly impossible to draw any distinct 

 boundary line between this No Man's Land and 

 the vegetable world on the one hand, or the 

 animal on the other, it appears to me that this 

 proceeding merely doubles the difficulty, which 

 before was single."* 



Here then is the argument ; because, forsooth, the 

 limitations of our senses, and the imperfections of our 

 means of research, make us to fail to distinguish 

 always clearly and accurately the boundary line, we 

 must simplify matters by denying that there is any 



* For a popular description of this " No Man's Land," see 

 the Introduction to Trouessart's " Microbes" &c. 



