PHYSIOLOGY OF THE LUNGS. 221 



the cervical ganglions, consisting of branches from the sym- 

 pathetic and the par vagum ; but, except under inflamma- 

 tion, these organs are not endowed with sensibility. Lym- 

 phatics are very plentifully distributed over them, and have 

 been successfully injected. 



THE PHYSIOLOGY OF THE LUNGS IN RESPIRATION, AND 

 AERATION OF THE BLOOD. 



Respiration. — The foetal colt subsists by juxta-position 

 between its own organs and the maternal, through the 

 medium of the placenta ; and it is by these secondary 

 means that its blood becomes partially aerated, for its 

 quiescent state would render perfect aeration injurious ; but 

 as soon as separated from the mother, an awful change 

 ensues. The foetus has hitherto reposed upon the softest 

 of all couches, which has been rendered more luxurious by 

 a temperature of a hundred degrees. Here it has slumbered 

 into life, when it is all at once awakened by the withdrawal 

 of the fluid within which it has rested. It is then squeezed, 

 and punched, and thumped by the violent contractions of 

 the uterus. It is next forced suddenly into a temperature 

 of say fifty degrees, or one half of that which it has been 

 used to ; when all at once the umbilical cord, which has 

 hitherto supplied it with breath, or enabled it to perform a 

 function similar to breathing, snaps, and the pains of suffo- 

 cation are undergone. It is under such circumstances the 

 little being makes a spasmodic struggle for life ; and the 

 lungs, hitherto passive, by a natural impulse are roused 

 into action : the muscles of the chest enlarge the cavity ; 

 the air rushes in, and the animal now breathes. The dis- 

 tention of the chest is a very important feature in respira- 

 tion, and is effected by an increase of several diameters ; 

 by the elevation of the ribs, and by the agency of the dia- 

 phragm. This last-named muscle in a state of rest is 

 convex towards the breast, and concave towards the abdo- 

 men ; but when its muscular fibres contract, it becomes 

 plane-like, which forcing backwards the abdominal viscera, 

 necessarily enlarges the thoracic cavity. The air re- 

 ceived into the lungs expands their cells, by which also the 

 blood finds a ready passage through their capillaries. The 

 lungs thus filled, an uneasy sensation stimulates them to 



