666 STIMULATION AND REGULATION OF THE RESPIRATORY CENTRE. 



causes slowing, and even arrest of the respiration (in expiration Rosenthal). 

 Arrest of the respiration in expiration is also caused by stimulation of the nasal 

 (Heriiut and KraUchmer) and ophthalmic branches of the trigeminus (Chrtstiani), 

 of the olfactory, and glossopharyngeal (Marchvald). [Kratschmer found that 

 tobacco-smoke blown into a rabbit's nostrils, or puffed through a hole in the 

 trachea into the nose, by stimulating the nasal branch of the fifth nerve, arrested 

 the respiration in the expiratory phase ; while it had no effect when blown into the 

 longs. Ammonia vapour applied to the nostrils arrests it iu the same way. If 

 ammonia vapour be blown into the lungs (the nasal cavity being protected from its 

 action), the respiration may be accelerated, or deepened, or arrested occasionally in 

 expiration, i.e., according to the fibres of the vagus acted on by the vapour in the 

 lungs {Knoll).'] Stimulation of the pulmonary branches of the vagus by breathing 

 irritating gases (Knoll) causes standstill in expiration, although some other gases 

 cause standstill in inspiration. Chemical stimulation of the trunk of the vagus, 

 by dilute solutions of sodic carbonate, causes expiratory inhibition of the respira- 

 tion ; and mechanical stimulation, rubbing with a glass rod, inspiratory inhibition 

 (Knoll). The stimulation of sensory cutaneous nerves, especially of the chest and 

 abdomen (as occurs on taking a cold douche), and stimulation of the splanchnics, 

 cause standstill in expiration, the first cause often giving rise to temporary clonic 

 contractions of the respiratory muscles. The respirations are often slowed to a very 

 great extent by pressure upon the brain, [whether the pressure be due to a 

 depressed fracture or effusion into the ventricles and subarachnoid space]. The 

 respiration may be greatly oppressed and stertorous. 



Tin- amount of work done by the respiratory muscles is altered during the reflex slowing of 

 the respiratory muscles, the work being increased during slow respiration, owing to the 

 ineffectual inspiratory efforts (Gad). The volume of the gases which passes through the lungs 

 during a given time remains unchanged (Valentin), and the gaseous exchanges are not altered 

 at first (Voit and Raubcr). 



Automatic Regulation. Under normal circumstances, it would seem that the 

 pulmonary branches of the vagus act upon the two respiratory centres, so as to set 

 in action what has been termed the self-adjusting mechanism ; thus, the inspiratory 

 dilatation of the lungs stimulates mechanically the fibres which reflexly excite the 

 expiratory centres, while the diminution of the lungs during expiration excites the 

 nerves which proceed to the inspiratory centre (Hering and Breuer, Head). [Thus, 

 blowing into the lungs excites the act of expiration, and sucking air out of them 

 excites inspiration.] 



In this way we may explain the alternate play of inspiration and expiration. In deep 

 narcosis, however, dilatation of the thorax in animals is followed first by cessation of the 

 respiratory movements, and then by inspiration (P. Guttmann). 



Discharge of the First Respiration. The foetus is in an apneeic condition 

 until birth, when the umbilical cord is cut. During intrauterine life, O is freely 

 supplied to it by the activity of the placenta. All conditions which interfere with 

 this due supply of O, as compression of the umbilical vessels and prolonged labour 

 pains, cause a decrease of the O and an increase of the C0 2 in the blood, so that 

 the condition of the foetal blood is so altered as to stimulate the respiratory centre, 

 and thus the impulse is given for the discharge of the first respiratory movement 

 (Schwartz). A foetus, still within the unopened foetal membranes, may make 

 respiratory movements (Vesalius. 1542). If the exchange of gases be interrupted 

 to a sufficient extent, dyspnoea and ultimately death of the foetus may occur. If, 

 however, the venous condition of the mother's blood develops very slowly, as in 

 cases of quiet slow death of the mother, the medulla oblongata of the foetus may 

 gradually die without any respiratory movement being discharged ( 324, 5). 



According to this view, the respiratory movements are due to the direct action of the 

 dyspneeic blood upon the medulla oblongata. [The excitability of the respiratory centre is less 



