CKOUP. 23 



order, and the pallor continues until, as palsy of the heart sets in, the 

 contents of the arteries grow less and less, the veins fuller and fuller, 

 and thus a livid tinge is imparted to the pallid lips. As the blood of 

 the veins within the thorax is subjected to a pressure less than that upon 

 the veins without, the tendency of the elastic lung being to contract, 

 and thus to cause the vessels which border upon it to expand ; as with 

 each deep inspiratory effort the power of suction of the lung grows 

 stronger (since the draught increases as the lung expands), this suction 

 must reach its highest pitch of intensity; blood will be drawn with 

 greatest power from the external veins into those within the thorax, 

 when any one with constricted glottis rarefies the air within his lungs by 

 trying to draw a long breath. Cyanosis and obstructed evacuation of 

 the cerebral veins can never take place in this way. The process must 

 always have an opposite effect. 



When inspiration and expiration meet with equal obstruction, the 

 circulation is somewhat differently affected. As the glottis becomes so 

 much occluded by false membrane that very little air can enter into, or 

 escape from, the lungs, inspiration and expiration can only be carried 

 on by means of all the auxiliaries at command. Now, as we are able 

 to expel our breath with greater force than we can inhale it, the influ- 

 ence of the forced expiration over the discharge of blood from the 

 thorax outweighs that of the forced inspiration, and then, indeed, cyano- 

 sis takes place. 4 



Since the interchange of gases in the lungs depends principally 

 upon the renewal of air contained in the air-vesicles, and as the blood 

 does not give out carbonic acid, and absorb oxygen, unless the air 

 within the vesicles contain less of carbonic acid and more of oxygen 

 than the blood in the plexus of capillaries about it, the necessary conse- 

 quence of the incomplete respiration in croup and of the imperfect ren- 

 ovation of the air in the vesicles is, that the carbonic acid which inces- 

 santly forms in the blood cannot escape from it into the air of the vesicles 

 which is already overcharged with it. The symptoms described are 

 exactly the same as those produced by the inhalation of carbonic acid. 

 In croup, the carbonic acid created within the body itself poisons the 

 patient, while in the other case the poison is breathed with the 

 atmosphere. 



In fatal cases, death almost always takes place with the symptoms 

 described, through the gradual establishment of general paralysis, in 

 consequence of carbonic-acid poisoning. In rare instances, the access 

 of air to the lungs may be suddenly and absolutely cut off by the fall 

 of a piece of loosened membrane before the glottis, and rapid death 

 by suffocation may ensue. 



If the croup take a turn for the better, the improvement may take 



