716 A MANUAL OF PHYSIOLOGY 



middle line in the floor of the fourth ventricle above the calamus 

 scriptorius is so related to the function of respiration that when 

 it is destroyed the animal ceases to breathe. But this respiratory 

 centre, the ' nceud vital ' of Flourens, does not correspond in position 

 with any definite collection of grey matter, although it includes the 

 nuclei of origin of several cranial nerves, and forms an important 

 point of departure for efferent, and of arrival for afferent, fibres con- 

 nected with the respiratory act. Its destruction involves the cutting 

 off of the impulses constantly travelling up the vagus to modify the 

 respiratory rhythm, and of the impulses constantly passing down the 

 cord to the phrenics and the intercostal nerves. And just as the 

 traffic of a wide region can be paralyzed at a single blow by severing 

 the lines in the neighbourhood of a great railway junction, or more 

 laboriously, though not less effectually, by separate section of the 

 same tracks at a radius of a hundred miles, so destruction of the 

 respiratory centre accomplishes by a single puncture what can be 

 also performed by section of all the respiratory nerves at a distance 

 from the medulla oblongata. But while nobody speaks of the 

 destruction of a 'centre' when a reflex action is abolished by 

 division of the peripheral nerves concerned in it, there is a tendency, 

 when the same effect is brought about by a lesion in the brain or 

 cord, to invoke that mysterious name, and to forget that the cerebro- 

 spinal axis is at least as much a stretch of conducting paths as a 

 collection of discharging nervous mechanisms. 



It is, perhaps, a profitless task to enumerate all the so-called 

 centres in the bulb and cord with which the perverse ingenuity of 

 investigators and systematic writers has encumbered the archives 

 and text-books of physiology. In addition to the great vaso-motor, 

 respiratory, cardio-inhibitory and cardio-augmentor centres in the 

 bulb, which, perhaps, have more right than the rest to be regarded 

 as distinct physiological mechanisms, if not as definitely bounded 

 anatomical areas, there have been distinguished ano-spinal, vesico- 

 spinal, and genito-spinal centres in the lumbar cord, a cilio-spinal 

 centre for dilatation of the pupil in the cervical cord, and in the 

 medulla centres for sneezing, for coughing, for sweating, for sucking, 

 for masticating, for swallowing, for salivating, for vomiting, for the 

 production of general convulsions, for closure of the eyes. It would 

 be just as correct, and more practically useful (for it would perhaps 

 encourage the student who has lost his way amidst these intermin- 

 able distinctions), to say that the cerebral cortex contains a centre 

 for learning sense, and another for forgetting nonsense, and that in 

 a healthy brain it is the latter which is generally thrown into activity 

 in the study of this portion of modern physiology = 



