THE RESPIRATORY CENTER AND NERVES. 751 



divided vagi causes arrest of respiration only upon the corresponding 

 side, while respiration continues upon the other side. The same result 

 is brought about if the trigeminal nerve upon one side is irritated. On 

 unilateral transverse division of the center the respiratory movement 

 ceases upon the side of the injury. 



According to Schiff the respiratory center is situated near the lateral margin 

 of the gray matter forming the floor of the fourth ventricle, extending posteriorly 

 not so far as the ala cinerea. According to Gierke and Heidenhain and others 

 that portion of the medulla, destruction of which is followed by cessation of respira- 

 tory movement is a single or double nerve-like strand, passing downward in the 

 substance of the medulla, within which, however, gray matter with small ganglia 

 is found. This is said to be constituted in part of the roots of the vagus, 'tri- 

 geminus, accessory and glossopharyngeal, connected with those of the oppo- 

 site side by means of fibers and extending downward into the cervical enlarge- 

 ment of the spinal cord. The strand thus connects as an intercentral bundle 

 the spinal cord (the seat of origin for the motor respiratory nerves) with the nuclei 

 of origin of the cerebral nerves named, the relations of which to the respiratory 

 movements are in part demonstrated. 



It is most probable that the dominating center that controls the rhythm 

 and the symmetry of the respiratory movements is situated in the medulla ob- 

 longata, but that in addition other centers of subordinate importance are situated 

 in the spinal cord and are controlled by the center in the medulla, receiving their 

 impulse to activity from that center. If in new-born animals the cord is divided 

 below the medulla by means of an exceedingly sharp instrument respiratory move- 

 ments of the chest will occasionally persist, from stimulation of the spinal cen- 

 ters, an observation that Landois was able to confirm in young dogs and cats. 



The spinal respiratory centers are, moreover, susceptible even to reflex in- 

 fluences (excitation or inhibition). Nitschmann divided the spinal center 

 situated in the upper cervical cord by means of a longitudinal section into two 

 equal parts, both of which then had an excito-respiratory influence upon the 

 diaphragm upon each side, even though the medulla just below the calamus 

 scriptorius had been divided upon one side.' Accordingly, the spinal centers of 

 both sides must be connected in the spinal cord. Irritation originating in one- 

 half of the center in the medulla may thus affect the spinal centers on both sides, 

 for example the origins of both phrenic nerves. The spinal center for the phrenic 

 nerve is situated between the third and seventh segments. 



In addition to the spinal cord, the brain also contains subordinate cerebral 

 respiratory centers. In the tissue between the striate body and the optic thalamus 

 I. Ott found a center, irritation of which markedly increased the number of respira- 

 tions. On destruction of this center the dyspneic respiratory acceleration (lieat- 

 dyspnea) induced by heat ceases. 



In the optic thalamus, on the floor of the third ventricle, Christiani found 

 further a special inspiratory center, which through stimulation of the optic and 

 auditory nerves, also after previous extirpation of the cerebrum and the striate 

 bodies, or also through direct irritation, causes deepening of inspiration and accel- 

 eration of respiration, and even arrest in inspiration. This inspiratory center can 

 be extirpated and it can then be demonstrated that a center controlling expiration 

 is situated in the substance of the anterior quadrigeminate body not far from 

 the aqueduct of Sylvius. Finally, the posterior quadrigeminate body contains a 

 second cerebral inspiratory center and also an inspiratory inhibiting center. Ob- 

 viously all of these centers are connected with the center in the medulla. 



According to Marckwald, the regular rhythm of the respiratory movements 

 is maintained, in addition to the posterior quadrigeminate bodies, also by the. 

 sensory nucleus of the trigeminus. 



The respiratory center consists of two central areas engaged in alter- 

 nate activity; the inspiratory and expiratory centers, of which each 

 forms the motor central point for the well-known group of inspiratory 

 and expiratory muscles. The center is an automatic one, for, even after 

 division of all of the sensory nerves that may exert a reflex influence upon 

 it, it preserves its activity. The irritability and the stimulation of the 

 center are dependent upon the state of the blood, particularly the amount 



