THE RESPIRATORY CENTER 325 



The chief service of the bronchial muscles is that when the intrabronchial 

 pressure rises, they give by their contraction a greater degree of firmness to 

 the bronchial walls. 



The mucous glands of the larynx and of the trachea receive their nerve 

 fibers through the laryngei nerves. In these also are afferent fibers which pro- 

 duce a reflex secretion of mucus in the larynx and trachea (Kokin). 



2. THE RESPIRATORY CENTER 



Since in the movements of respiration a large number of muscles contract 

 in a definite sequence, it is to be assumed in conformity with our present 

 views of innervation, that somewhere in the central nervous system is a center 

 controlling these movements. 



From the fact that these movements 'do not cease when the brain is cut 

 through as high up as the pons, it follows that the respiratory center must 

 be situated below that point i. e. ? not higher than the medulla. When such 

 a section is made, the diaphragm stops for a moment, but begins of itself 

 to contract, and continues quite regularly unless some unintentional lesion 

 has occurred. 



When, on the other hand, the medulla is separated from the spinal cord, 

 respiration ceases. Galen knew that in the upper part of the spinal cord there 

 is a place the destruction of which at once stopped respiration, and Le Gallois 

 (1812) showed that this spot is in the medulla. For a long time it was 

 generally agreed that the respiratory center was to be sought only in the 

 medulla. Recently, however, it has been claimed with great positiveness that, 

 although there is a regulatory apparatus' in the medulla, the true centers' for 

 the respiratory movements are to be sought in the spinal cord, and the advo- 

 cates of this doctrine go so far as to say that the nuclei of the respiratory 

 nerves are stimulated simultaneously by the blood, thus giving the impulse 

 for a coordinated respiratory activity (Brown-Sequard, Langendorff, Wert- 

 heimer). The stoppage of respiration after section of the cervical cord would, 

 in their opinion, be due not to separation of the respiratory nerves from their 

 center, but to the shocklike, inhibitory effect of the section. 



There are numerous experiments which show that direct stimulation of the 

 spinal cord with electricity or by mechanical means may stop respiration, and 

 the view just mentioned is well supported by such facts. But it is at present 

 impossible to decide how long such an effect of shock may last. If an animal 

 whose cord has been sectioned in the neck be maintained by artificial respira- 

 tion, it can be kept alive for hours. But if the animal still does not breathe 

 spontaneously one cannot refute the claim that shock still persists. 



In cases where artificial respiration is first maintained for a long time, 

 rhythmical respiration has been observed on animals with the cord severed in 

 the neck. Some of the first observations of this kind were made on newly born 

 animals and some on animals whose reflex irritability had been artificially in- 

 creased with strychnia (Rokitansky, Langendorff). Later Wertheimer succeeded 

 in obtaining spinal respiration in grown animals which had not been poisoned. 

 But when spinal respiration does appear it is never of the same extent as that 

 controlled from the medulla, and it continues, so far as is yet known, at most 



