42 NATURAL BODIES. 



irritability, the nature of which will fall under consideration here- 

 after. It is possessed equally by animals and vegetables, and is essen- 

 tially organic and vital. This power, we shall see, needs not the 

 intervention of volition: it is constantly exerted in the animal without 

 consciousness, and therefore necessarily without volition. Its existence 

 in vegetables does not, consequently, demonstrate that they are pos- 

 sessed of consciousness. 



4. Nutrition. A great difference exists between plants and animals 

 in ^this respect. The plant, being fixed to the soil, cannot search after 

 food. It must be passive ; and obtain its supplies from the materials 

 around, and in contact with it ; and the absorbing vessels of nutrition 

 must necessarily open on its exterior. In the animal, on the other 

 hand, the aliment is scarcely ever found in a state fit for absorption : 

 it is crude, and in general Ehrenberg 1 thinks always requires to be 

 received into a central organ or stomach, for the purpose of under- 

 going changes, by a process termed digestion, which adapts it for the 

 nutrition of the individual. The absorbing vessels of nutrition arise, 

 in this case, from the internal or lining membrane of the alimentary 

 tube. The analogy that exists between these two kinds of absorption 

 is great, and had not escaped the attention of the ancients* Quem- 

 admodum terra arboribus, ita animalibus ventriculus sicut humus," 

 was an aphoristic expression of universal reception. With similar 

 feelings, Boerhaave asserts, that animals have their roots of nutrition 

 in their intestines ; and Dr. Alston 2 has fancifully termed a plant an 

 inverted animal. 



After all, however, the most essential difference consists in the steps 

 that are preliminary to the reception of food. These, in the animal, 

 are voluntary, requiring prehension ; often locomotion ; and always 

 consciousness. 



5. Reproduction. In this function we find a striking analogy be- 

 tween animals and vegetables ; but differences exist, which must be 

 referred to the same cause that produced many of the distinctions 

 already pointed out, the possession, by the animal, of sensibility and 

 locomotility. For example, every part of the generative act, as before 

 remarked, is, in the vegetable, without the perception or volition of the 

 being: the union of the sexes, fecundation, and the birth of the new 

 individual are alike automatic. In the animal, on the other hand, the 

 approximation of the sexes is always voluntary and effected consciously : 

 the birth of the new individual being not only perceived, but some- 

 what aided by volition. Fecundation alone is involuntary and irre- 

 sistible. 



Again, in the vegetable the sexual organs do not exist at an early 

 period ; and are not developed until reproduction is practicable. They 

 are capable of acting for once only, and perish after fecundation ; and 

 if the plant be vivacious, they fall off after each reproduction, and are 

 annually renewed. In the animal, on the contrary, they exist from the 

 earliest period of foetal development, survive repeated fecundations, 

 and continue during the life of the individual. 



1 Edinb. New Philosophical Journal, for Sept. 1831 ; and Jan. 1838, p. 232. 

 a Tirocinium Botanicum Edinburgense, 8vo., Edinb. 1753. 



