REFLEX ACTIONS. RESPIRATORY MOVEMENTS. 293 



during sleep or profound attention, when the influence of the Encephalon is 

 more or less suspended. 



375. But why (it may be asked) do the movements continue, when the 

 Pneumogastrics have been divided, and the Encephalon has been removed ? 

 It is evident that there must be other exciters to the action of the respiratory 

 muscles. Amongst these, the nerves distributed to the general surface, and 

 particularly to the face, probably perform an important part; and in exciting 

 the first inspiration, the Fifth pair seems the principal agent. It has long 

 been a well-known fact, that the first inspiratory effort of the new-born infant 

 is most vigorously performed, when the cool external air comes into contact 

 with the face ; and that impressions on the general surface, such as a slap of 

 the hand on the nates, are often effectual in exciting the first inspiratory 

 movements, when they would not otherwise commence. Dr. M. Hall relates 

 an interesting case, in which the first inspiration was delayed, simply because 

 the face was protected by the bed-clothes from the atmosphere; and, on lift- 

 ing up these, the infant immediately breathed. Dr. M. Hall has recently 

 mentioned the important fact, that if the cerebrum be removed, and the pneu- 

 mogastrics be divided, in a young kitten, the number o*f acts of respiration 

 will be reduced to four in a minute; but by directing a stream of air on the 

 animal, or by irritating various parts of the general surface, we may excite 

 twenty or thirty acts of respiration within the same space of time. He 

 further remarks, that in the very young warm-blooded animal, as in the cold- 

 blooded animal, the phenomena of the excito-motor power are far more vividly 

 manifested, than in the older and the warm-blooded. In the very young 

 kitten, even when asphyxiated to insensibility, every touch, contact, or slight 

 blow, every jar of the table, any sudden impression of the external air, or 

 that of a few drops of cold water, induces at once energetic reflex movements, 

 and acts of inspiration. This may be looked upon as Nature's provision for 

 the first establishment of the acts of inspiration in the new-born animal. 

 But the influence of the nerves of the general system is by no means want- 

 ing in the adult; as the following experiment of Dr. J. Reid's demonstrates. 

 After dividing the pneumogastrics, and removing the cerebrum and cerebel- 

 lum, he divided the spinal cord high up in the neck, so as to cut off the com- 

 munication between the spinal nerves and the Medulla Oblongata ; and he 

 found that the frequency of the respiratory movements was still further 

 diminished, although they were not even then entirely suspended. Every 

 one knows the fact, that the first plunge into cold water, the first descent of 

 the streams of the shower-bath, or even the dashing of a glass of cold water 

 in the face, will produce inspiratory efforts ; and this fact has many important 

 practical applications. Thus in the treatment of Asphyxia, whether congeni- 

 tal, or the result of narcotic poisoning, drowning, &c., the alternate applica- 

 tion of cold and heat is found to be one of the most efficacious means of 

 restoring the respiratory movements; and a paroxysm of hysteric laughter 

 may be cut short, by dashing a glass of cold water in the face. It may be 

 surmised that the Sympathetic nerve, which derives many filaments from the 

 Cerebro-Spinal system, and which especially communicates with the Pneu- 

 mogastric nerves, is one of the excitors to this function; and this, perhaps, 

 not only through its ramifications in the lungs, which are considerable, but 

 also by its distribution on the systemic vessels; so that it may convey to the 

 Spinal Cord the impression of imperfectly-arterialized blood, circulating in 

 these, such as the Pneumogastric is believed to transmit from the lungs. It 

 will hereafter be shown, that an impression of a corresponding kind is more 

 probably the cause of the sense of Hunger and Thirst, than any which origi- 

 nates in the stomach alone (Chap. X., Sect. 1). 



376. The Motor or Efferent nerves concerned in the function of Respira- 



26* 



