ANIMALS AND PLANTS DEFINED. 3 



In general terms it may be stated that Animals are liv- 

 ing beings ivhich are nourished and built up wholly l>y 

 organic food that is, by vegetable and animal materials 

 and which have sensation and the power of voluntary 

 motion, and which consume oxygen and give off carbonic 

 acid. 



Plants are organisms which are endowed with life proba- 

 bly as real as that of animals, and perhaps differing from 

 that of the latter only in degree; but, unlike animals, 

 they are sustained and built up by inorganic nutriment 

 that is, by earthy materials, water, and gases and they 

 consume carbonic acid and give off oxygen.* Although it 

 probably cannot be said that they have true sensation, they 

 seem to have something analogous to sensation ; and it is 

 now generally maintained by botanists that all plants 

 have spontaneous motion. Such motion, however, is in 

 most cases too slow for our observation. Yet much has 



in one or the other of these two kingdoms of life. But it must be said that 

 there are organisms which at one period of their life exhibit an aggregate of 

 phenomena such as to justify us in speaking of them as animals, whilst at 

 another they appear to be as distinctly vegetable. A monad [Page. 491] may 

 at one period be possessed not only of a nucleus and contractile vacuole, 

 but of a cilium, by the aid of which it swims about ; at another it may have 

 lost its cilium and effect locomotion by the protrusion of pseudopodia like 

 an Amoeba ; whilst in a third it may surround itself with an envelope of 

 cellulose. If it should prove to be true that organisms as high in the scale as 

 the Amcebina [Fig. 746] and Actinophryna [Fig. 752], can have their develop- 

 ment traced back to the specialization of protoplasm within vegetable cells, 

 it would appear to be necessary to adopt a phraseology which should speak 

 of such creatures as being at one time plants and at another animals." 

 Rolleston, " Forms of Animal Life.' 1 ' 1 



* As to the relations of oxygen and carbonic acid to living plants and ani- 

 mals, it must be stated here that the definitions given above have to be modi- 

 fied by the fact that Wohler claims to have shown that some kinds of the 

 Infusoria give off oxygen instead of consuming it, as is done by animals in 

 general ; and that Schlossberger and Dopping claim to have shown that 

 some kinds of mushrooms exhale carbonic acid instead of consuming it, as 

 is done by most species of plants. 



