RESPIRATORY MOVEMENTS AT BIRTH 277 



is set to act by the condition of its metabolism, much in the same way as 

 the heart is set to beat rhythmically. When anabolism is completed, catab- 

 olism or discharge occurs, and this alternate but crude and spasmodic 

 action will occur without a definite blood supply so long as the centers are 

 properly nourished and stimulated by their own intercellular fluid. It is 

 unreasonable to think, however, that the respiratory center is independent 

 of the character of the blood supply, either as regards quantity or quality 

 of the blood. It has also been shown that the presence of the products of 

 great muscular metabolism in the blood will greatly increase the irritability 

 of the respiratory center, even if the blood itself be not particularly venous 

 in character. 



The Establishment of Respiratory Movements at Birth. From 

 the preceding paragraph it appears that the regulation of the respiratory 

 movements is normally due to the automaticity of the respiratory center as 

 influenced, first, by the blood flowing through it and, second, by the afferent 

 nerve impulses which reach the center. The fetus in the womb is supplied 

 by arterial blood from the blood-vessels of the mother. The fetus does not 

 ordinarily give respiratory movements before birth, but it may be made to 

 do so by experimental procedure. At birth the placental circulation is sud- 

 denly interrupted, and the blood rapidly increases in venosity until the skin, 

 lips, and mucous membranes are very cyanotic in appearance. It is at this 

 time that the respiratory center begins its rhythmic discharges, being aroused 

 by the direct stimulating effects of the strongly venous blood. It is more 

 than possible that the irritability of the center is also increased by the stimu- 

 lation of the skin by the air, the contact with clothing, and the hands of the 

 nurse. We have already seen that cutaneous stimulation leads to increase 

 in both respiratory rate and amplitude even in the adult. The primary 

 stimulus for the establishment of the respiratory rhythm at birth, then, is 

 the venosity of the blood, but this cause is supported by the general reflexes 

 which reach the respiratory center. 



Certain Special Types of Respiration. Whatever the exact quality 

 of the venous blood which excites the respiratory center to produce normal 

 respirations, there can be no doubt that, as the blood becomes more and more 

 venous from obstruction to the entrance of air into the lung, or from the 

 blood not taking up from the air its usual supply of oxygen, the respiratory 

 center becomes either less or more active and excitable. Conditions ensue 

 which have received the names Apnea (diminished breathing), Hyper pnea 

 (excessive breathing), Dyspnea (difficult breathing), and Asphyxia (suffoca- 

 tion). 



Apnea. This is a condition of diminished respiratory movement. When 

 we take several deep inspirations in rapid succession by voluntary effort, 

 we find that we can do without breathing for a much longer time than usual; 

 in other words, several rapid respirations seem to inhibit for a time normal 



