VHYSIOLOGY. 489 



3017. Towards the termination of pregnancy, when 

 the foetus is endowed with muscular motion, the foetal 

 water is also absorbed. Nutrition is therefore in the 

 commencement an absorption carried on by the integu- 

 ment, and lastly by the intestine. 



2. Respiration. 



3018. The respiratory organ of the foetus is the cho- 

 rion, and in particular the placenta. Its tissue is like 

 that of the branchiae or spleen. 



3019. The arterial blood transmitted through the 

 umbilical vein is conducted through the foramen ovale 

 into the left ventricle of the heart, and from thence 

 directly to the principal organ of the foetus, the brain 

 and spinal cord. From hence it returns, venous in 

 quality, to the right side of the heart, and from thence 

 through the cluctus arteriosus into the inferior or de- 

 scending aorta, from which, pursuing its course through 

 the umbilical arteries, it again reaches the placenta, in 

 which it undergoes a renewed oxydation. 



3020. If therefore the umbilical cord be compressed, 

 the foetus dies suddenly, as happens indeed accidentally 

 in certain cases, which completely resemble those of 

 death produced by suffocation. The chick when in the 

 egg dies, if the egg-shell be coated over with varnish, or 

 if the egg be submitted to the noxious influence of gases 

 which are devoid of oxygen. 



3021 . The respiration effected through means of the 

 placenta, admits also of being proved by the sudden 

 change which occurs in the circulation after birth. No 

 arterial blood being then any longer brought to the heart 

 through the umbilical vein, the left heart is no longer 

 stimulated, and the foramen ovale collapses and is 

 closed. Thus, all the blood enters the right side of the 

 heart, and finding no thoroughfare into the ductus arte- 

 riosus, it is driven forcibly into the lungs, which now 

 expand, and thereby leave an empty space between the 

 pulmonary vessels, into which the air rushes in. 



3022. The first act of respiration is therefore the 



