122 VASCULAR SYSTEM. 



ovale and ductus arteriosus; the chemical change is the 

 action of the air on the blood in the lungs. 



Q. How does respiration commence at birth? 



#. In consequence of a general excitement produced on 

 all the moving parts from external impression at birth; 

 perhaps the intercostals and diaphragm are set in motion 

 instinctively. 



Q. Are you correct in applying the term instinct in 

 this case? 



<A. Yes; for various examples of these instinctive ac- 

 tions at birth can be presented. Observe, the infant pre- 

 pares it mouth for sucking; animals seek the teats of the 

 mother; gallinaceous animals look for grain, &c. to nou- 

 rish them. 



Q. But as the ductus arteriosus is not entirely closed 

 at birth, how is it that blood does not pass through it? 



Ji. It is accounted for in two ways; the capillaries of 

 the lungs invite blood through the pulmonary artery, and 

 the vital forces of the duct itself are offended by blood 

 which is not placental; thus the blood goes on to the 

 lungs. 



Q. How is the, foramen ovale closed? 



#. When the blood passes from the pulmonary veins 

 into the left auricle, one valve of the foramen is pressed 

 on the opening; and when the blood comes from the cavas 

 into the right auricle, the two valves are completely united, 

 and kept so till union permanently takes place. 



Q. Can the foramen ovale remain open and the circula- 

 tion go on? 



*#. It can. Bichat has repeatedly seen it; for, though 

 open, the auricular contraction so throws the valves of the 



