CHAP. I.] OF A NERVOUS SYSTEM. 9 



up a state of excitation in the tissues of the plant. Simi- 

 larly, there must be some definite molecular relation 

 between a magnet and pieces of iron or steel, leading to 

 their ' selection ' whenever they come within certain degrees 

 of proximity. In the latter case we have, unquestionably, 

 to do with problems of molecular physics ; and in the case 

 of the affinity which seems to exist between the nerveless 

 Amoeba and the organic fragments or minute living things 

 which it absords as food, we probably have to do with an 

 allied problem. There may be differences of degree, but 

 none of kind ; all must be included as problems of mole- 

 cular physics. 



At any rate, be the cause what it may, the coming into 

 contact of a fragment of organic matter with projected 

 portions of the substance of an Amoeba is followed by the 

 closure of this mobile substance round it. The organic 

 mass is gradually drawn into the interior of our Proteus, 

 where, after being thus appropriated, it slowly disappears 

 by a rudimentary process of ' digestion.' After feeding, 

 in this way, and assimilating the organic matter taken into 

 its interior, the Amoeba rapidly increases in size, and per- 

 haps still continues its active movements. Or, as 

 happens at other times, its movements may cease : the 

 creature grows sluggish from over-feeding, and then, as a 

 consequence of its motionless condition, its outer layer 

 soon becomes differentiated into a cyst-wall. 



Simple as this mode of nutrition may appear to those 

 who are familiar with it, its initiation in the Amoeba is 

 followed by consequences of the most profound importance. 

 The assimilation, after such a fashion, of already elaborated 

 organic matter is strongly calculated to increase that high 

 degree of vitality which originally led the organism to 

 take in solid food. This mode of nutrition, in fact, entails 

 a liberation within the organism of much of the molecular 



