1078 PHYSIOLOGY 



THE QUESTION OF SPINAL RESPIRATORY CENTRES. Several physiologists 

 e.g. Brown Sequard, Langendorff, and Wertheimer, have described respiratory centres 

 in the spinal cord. There is no doubt that if the cord be cut across in the upper cervical 

 region, and artificial respiration maintained for some time, cessation of the respiration 

 may be followed by rhythmic contractions of the respiratory muscles. These are 

 especially marked in young animals and if the activity of the cord has been heightened 

 by the injection of small doses of strychnine. Careful observation of the movements 

 shows, however, that they cannot be spoken of as respiratory, since although rhythmic, 

 they are not co-ordinate. The diaphragm may contract either simultaneously or in 

 alternation with the intercostals, and muscles which are essentially expiratory at the 

 same time as those which we are wont to regard as inspiratory. These experiments 

 show merely that the motor centres of the cord can enter into rhythmic activity under 

 the influence of asphyxial conditions. The movements affect the muscles of the limbs 

 as well as those essentially respiratory in function. 



THE AUTOMATICITY OF THE RESPIRATORY CENTRE 



We have now to inquire what it is that keeps the respiratory centre in 

 activity. Is the rhythmic discharge of inspiratory impulses from the centre 

 due to rhythmic or continuous stimulation of afferent nerves, or is the centre 

 so constructed that under the normal conditions of its environment the 

 metabolic activity of its constituent parts tends, like that of the heart- cells, 

 to assume a rhythmic character ? In other words, is the activity of the centre 

 reflex or automatic ? It has been found by Rosenthal that rhythmic respira- 

 tory movements are maintained even after complete section of the brain- 

 stem at the level of the superior corpora quadrigemina, section of the cord 

 at the level of the seventh cervical nerve, and division of both vagi and of the 

 posterior roots of all the cervical spinal nerves. It is true that if the sections 

 of the brain-stem be placed as low as the strice acousticce, the respiratory 

 movements are profoundly modified and give place to a series of inspiratory 

 spasms. We might argue from this that the centre was capable of a very 

 imperfect degree of automatic action, but needed the stimulus of afferent 

 impulses from the vagi or from the higher parts of the brain to render these 

 actions adequate for the respiratory needs of the organism. 



In the above experiment the centre cannot be regarded as free from all 

 afferent stimuli, since the mere closure of the demarcation current in the 

 cut ends of the nerves would cause a certain amount of excitation, and the 

 animal does not survive sufficiently long to allow this condition to pass off. 

 Hering has shown that in the ( spinal cord frog ' (i.e. one in which the brain 

 has been destroyed) section of all the posterior roots absolutely destroys 

 all mobility, the injection of strychnine being without effect. A typical 

 spasm, however, can be at once produced by exposing and stimulating the 

 stump of one of the cut posterior roots. We might suppose that the respira- 

 tory centre would be similarly devoid of automatism if absolutely free from 

 afferent stimuli. It must be mentioned, however, that according to Sherring- 

 ton it is possible to excite strychnine or asphyxial spasms in a dog or cat 

 with isolated spinal cord, in which all the afferent roots below the transection 

 have been divided six or seven hours previously. He therefore is of opinion 

 that in the mammal the motor nervous mechanism can be set into activity 



