532 GENERAL OBSERVATIONS. 



In the course of time, however, this branch of the aorta is 

 contracted, so that no fluid passes through it ; and it has 

 the appearance of a ligament, in which state it remains. 



The course of the blood from the right ventricle, through the 

 pulmonary artery to the aorta below its curve, is more direct 

 than that from the left ventricle to the same spot through the 

 aorta at its commencement. The column of blood in the aorta 

 below its curve is evidently propelled by the force of both 

 ventricles: and this circumstance, although it seems to pro- 

 ceed merely from the state of the foetal lungs, is particularly 

 calculated for the very extensive circulation which the foetus 

 carries on, by means of the umbilical arteries and vein in the 

 placenta. 



The Lungs of the Fceius 



Differ greatly from those of the adult. They appear solid, 

 as if they were composed of the parenchymatous substance 

 which constitutes the matter of glands, rather than the light spongy 

 substance of the lungs of adults. They differ also in color from 

 the lungs of older subjects, being of a dull red. 



They have greater specific gravity than water ; but if air be 

 once inspired, so much of it remains in them that they ever 

 afterwards float in the former fluid. 



The nature of the process of respiration, and its effects upon the animal 

 economy, particularly upon the action of the heart, appear to be much better 

 understood at this time than they were before the discovery of the composition 

 of the atmosphere, by Dr. Priestley and Mr. Scheele. The publications upon 

 this subject, which have appeared since that period, namely, 1774, are there- 

 fore much more interesting to the student of medicine than those which 

 preceded them. Two of these publications ought to be particularly noticed 

 by him ; namely, an essay, by Dr. Edward Goodwyn, entitled, " The Con- 

 nexion of Life with Respiration ; " — and the " Physiological Researches of 

 M. Bichat upon Life and Death." Part Second.* 



The general doctrines respecting the oxygenation or decarbonization of the blood 

 and the absolute necessity that it should take place to a certain degree in 



* The student will derive much information respecting the publications on this subject, 

 prior to 1804, from Dr. Bostock's Essay on Respiration. — Since the publication of that essay 

 several interesting papers on respiration have appeared, namely, Two Memoirs by the late 

 Abbe Spallanzani; " An Inquiry into the Changes induced on Atmospheric Air by the Ger- 

 mination of seeds," itc, by Ellis ; two very important communications by Messrs. Allen and 

 Pepys in the Transactions of the Royal Society of London for 1808 and 1809 ; and " Farther 

 Inquiries into the Changes induced on Atmospheric Air," also by Ellis. 



