398 OF FOOD, AND THE DIGESTIVE PROCESS. 



being performed under the same essential conditions as the purely " consensual" 

 or " sensori-motor" actions. 1 The necessity of guiding sensations for their 

 performance is made evident by one of Sir C. Bell's experiments, the wrong 

 interpretation of whose results originally led him to an erroneous view of the 

 functions of the Fifth pair of nerves. He found that an Ass, in which the 

 infra-orbital branch of this nerve had been divided, made no attempt to pick up 

 oats with its lip, although the animal saw them, bent down its head with the 

 obvious purpose of ingesting them, and brought its lip into absolute contact 

 with them; hence he concluded that the power of motion was destroyed in the 

 lip, when it was in reality only the guiding sensation that was deficient, the 

 motor power being supplied by the Facial nerve or Portio dura. But although 

 the movements concerned in the ingestion of food in the adult require the co- 

 operation of the sensorial centres, this is not the case with the act of suction in 

 the Infant, which may be considered as essentially a respiratory act, and which 

 is performed not merely without will, but even without consciousness. The ex- 

 periments provided for us by nature, in the production of Anencephalous mon- 

 strosities, fully prove that the " nervous circle" whereby the lips and respiratory 

 organs are connected with the Medulla Oblongata, is alone sufficient for its per- 

 formance ; and Mr. Grainger has sufficiently established the same, by experiment 

 upon puppies whose brain had been removed. He adds that, as one of these 

 brainless puppies lay on its side, sucking the finger which was presented to its 

 lips, it pushed out its feet in the same manner as young pigs exert theirs against 

 the sow's dugs. 3 The Human infant or other young Mammal, however, performs 

 movements which are of a higher character than this; going in search, as it were, 

 of the source of its nourishment; towards which it seems to be especially 

 guided by the sense of Smell. Such movements are probably to be considered 

 as " consensual," and as deriving their first stimulus from tlie internal feelings 

 of hunger, whilst their direction is given by the guiding sensation which indi- 

 cates the situation of the appropriate aliment. That no such actions are called 

 into play by the same stimuli, after the expiry of the period during which the 

 young Mammal is dependent upon its maternal parent for its nourishment, 

 seems to indicate that the reactive power of the nervous centres on which they 

 are dependent is only temporary, and that it ceases with the need for its exer- 

 cise ; the child growing-out (so to speak) of this automatic power, whilst it grows- 

 into many new ones those especially, which are connected with the generative 

 function. 



424. The food thus introduced into the mouth, is subjected (unless it be al- 

 ready in a state which needs no further reduction) to the process of Mastication. 

 This is evidently an operation of great importance in preparing the substances 

 to be afterwards operated on for the action of their solvent; and it exactly cor- 



1 This, the Author thinks, will be conformable to the experience of most of his readers ; 

 who will find, if they analyze their own consciousness, that they continue to eat while their 

 whole attention is given to some abstract train of thought, or to some external object. But 

 a remarkable case will be cited hereafter. (CHAP. xiv. SECT. 7), which fully confirms the 

 view here advanced ; the movements, not merely of the lips and jaws, but those by which 

 food was conveyed to the mouth, having been carried on automatically, when once (so to 

 speak) the spring was touched by which they were set in action. 



2 "Observations on the Structure and Functions of the Spinal Cord," pp. 80, 81. The 

 actions of the mammary foetus of the Kangaroo, described by Mr. Morgan, furnish a very 

 interesting exemplification of the same function of the Spinal Cord ; this creature, resem- 

 bling an earth-worm in appearance, and only about fourteen lines in length, with a brain 

 corresponding in degree of development to that of a human foetus of the ninth week, 

 executes regular, but slow, movements of respiration, adheres firmly to the point of the 

 nipple, and moves its limbs when disturbed. The milk is forced into the oesophagus by a 

 compressor muscle, with which the mamma of the parent is provided. "Can it be im- 

 agined," very justly asks Mr. Grainger, "that in this case there are sensation and volition, 

 in what can be proved anatomically to be a foetus ?" 



