754 THE RESPIRATORY CENTER. 



movements or increased these if already present. Langendorf observed in con- 

 sequence of electrical, mechanical or chemical irritation (with salt) generally an 

 expiratory effect; on the other hand, after irritation of the cervical cord (sub- 

 ordinate center), an inspiratory effect. According to Laborde, a superficial lesion 

 in the neighborhood of the apex of the calamus scriptorius causes arrest of the 

 respiratory movements of a few minutes' duration. 



If arrest of the heart is caused by irritation of the peripheral stump of the 

 divided vagus, arrest of respiration for a few seconds ensues at the same time. 

 In consequence of the arrest of the heart, transitory anemia occurs, as a result 

 of which the irritability of the respiratory center is diminished, so that respiration 

 ceases for a time. The observations of Ahlfeld are most remarkable, in which in 

 spite of abolition of the action of the heart in the new-born the respiratory move- 

 ments still persisted, as in dogs after poisoning with antiar. 



Reference has already been made to the great correspondence in the regula- 

 tion of the respiratory and the intestinal nervous systems (p. 288). 



In addition to direct irritation of the respiratory center locally, it 

 may be influenced also by the will and reflexly through a number of cen- 

 tripetal nerves. 



Through the will it is possible to suppress the breathing for only 

 a short time, that is until the increased venosity of the blood excites the 

 respiratory center to renewed activity. The number and the depth of 

 the movements can be increased for a considerable time ; in addition the 

 will has an influence upon the rhythm. The influence of the cerebral 

 cortex upon the respiration is considered on p. 790. 



The respiratory center can be influenced reflexly, and there are 

 both excitor and inhibitory nerves. The nerves through which the 

 respiratory center is stimulated reflexly are contained in the pulmonary 

 branches of the vagus, also in the sensory nerves of the eye, the ear, and 

 the skin. Under normal conditions their action preponderates over that 

 of the inhibitory nerves. Thus, for example, a cold bath makes the 

 respirations deeper and thus causes moderate acceleration of pulmonary 

 ventilation. 



Influence of the Vagus. Division of the vagus on both sides causes, in con- 

 sequence of removal of the influence of these stimulating fibers, slowing of the 

 respiratory movements. Under such circumstances, the entire amount of air ex- 

 changed remains for a time unchanged, but respiration is deepened and takes 

 place with excessive and inadequate inspiratory effort. In agreement with experi- 

 mental section, subsequent feeble tetanizing irritation of the central stump of the 

 vagus is again followed by acceleration of the respiratory movements. More 

 marked irritation causes arrest of breathing in inspiration or (particularly when 

 the nerve is exhausted) in expiration. Irritation of the sensory nerves of the 

 thoracic and abdominal wall causes retardation of breathing when both vagi are 

 divided. 



According to Lewandowsky slight irritation of the central stump of the vagus 

 by means of induced currents causes diminished depth of inspiration. Then, as 

 the strength of the current is increased, respiration becomes accelerated. A still 

 stronger irritation causes the thorax to assume the inspiratory position, then 

 arrest in inspiration and finally irregular restlessness of the respiratory move- 

 ments i the constant current be employed, closure of an ascending current or 

 (in chloral-narcosis) an uninterrupted ascending current applied to the central 

 stump of the vagus causes arrest of breathing in expiration or slowing of the 

 respiratory rhythm (inhibitory effect); while an interrupted descending current, 

 as well as closure of descending current, cause arrest of breathing in inspiration, 

 or acceleration of breathing (stimulating effect) . 



^ Chemical irritation of the central stump of the vagus by means of sodium 

 did or potassium chlorid causes expiratory arrest of breathing. Momentary 



;ant influences cause inspiratory, continued irritation, expiratory effects. The 

 active fibers are situated in the uppermost root-bundles of the centers of the 

 ninth, tenth and eleventh nerves in the rabbit 



