OF VITAL ACTIONS, AND THEIR MUTUAL DEPENDENCE. 75 



in the former the stimulus is applied to the contractile part itself, whilst in the 

 latter it is applied to an organ with which this is connected by nerves only. 

 Now we have, even in Vegetables, instances of the propagation of an irrita- 

 tion from one part to another, so that a motion results in a part distant from 

 that stimulated, as in the case of the Sensitive Plant, or Venus's Fly-trap. 

 The only essential difference, therefore, between those movements of Animals, 

 which are thus closely connected with the maintenance of the organic func- 

 tions, and those of Plants, consists in the medium through which they are 

 performed, this being in Animals the Nervous and Muscular apparatus, 

 whilst in Plants it is only a peculiar modification of the ordinary structure. 



81. From what has been said, then, it appears that all the functions of the 

 Animal body are so completely bound up together, that none can be suspended 

 without the cessation of the rest. The properties of all the tissues and organs 

 are dependent upon their regular Nutrition by a due supply of perfectly ela- 

 borated blood; this cannot be effected, unless the functions of Circulation, 

 Respiration and Secretion, be performed with regularity, the first being 

 necessary to convey the supply of nutritious fluid, and the tw r o latter to sepa- 

 rate it from its impurities. The Respiration cannot be maintained without the 

 integrity of a certain part of the nervous system ; and the due action of this, 

 again, is dependent upon its regular nutrition. The materials necessary for 

 the replacement of those, which are continually being separated from the blood, 

 can only be derived by the Absorption of ingested aliment ; and this cannot 

 be accomplished, without the preliminary process of Digestion. The intro- 

 duction of food into the stomach, again, is dependent, like the actions of Re- 

 spiration, upon the operations of the muscular apparatus and of a part of the 

 nervous centres; and the previous acquirement of food necessarily involves 

 the purely Animal powers. Now it will serve to show the distinction between 

 these powers, and those which are merely subservient to Organic life, if we 

 advert to the case, which is of no unfrequent occurrence, of a human being, 

 deprived by some morbid condition of the brain, of all the powers of Animal 

 life, Sensation, Thought, Volition, &c. ; and yet capable of maintaining a 

 vegetative existence, all the organic functions going on as usual, the morbid 

 condition not having affected the division of the nervous system that is con- 

 cerned in the movements on which some of them depend. It is evident that 

 we can assign no definite limits to such a state, so long as the necessary food 

 is placed within the reach of the grasp of the muscles, that will convey it into 

 the stomach : as a matter of fact, however, it is seldom of long continuance ; 

 since the disordered state of the brain is sure to extend itself, sooner or later, 

 to the rest of the nervous system. This condition may be experimentally imi- 

 tated, however, by the removal of the brain, in many of the lower animals, 

 whose bodies will sustain life for many months after such a mutilation ; but 

 this can only take place, when that food is conveyed by external agency, within 

 the pharynx, which they would, if in their natural condition, have obtained 

 for themselves. A similar experiment is sometimes made by Nature for the 

 physiologist, in the production of fo3tuses, as well of the human as of other 

 species, in which the brain is absent ; these can breathe and suck and swal- 

 low, and perform all their organic functions ; and there is no assignable limit 

 to their existence, so long as they are duly supplied with food. Hence we 

 may learn the exact nature of the dependence of the Organic functions upon 

 those of purely Animal life ; and we perceive that, though less immediate than 

 it is upon the simple organic operations of the nervous and muscular systems, 

 it is not less complete. On the other hand, the functions of Animal life are 

 even more closely dependent upon the Nutritive actions than are those of or- 

 ganic life in general ; for many tissues will retain their several properties, and 

 their power of growth and extension, for a much longer period after a general 



