'~70
MRS. B.
I cannot answer this question without enteringinto an explanation of the nature and structure ofthe lungs. You recollect that the venous blood,on being expelled from the right ventricle, entersthe lungs to go through what we may call thelesser circulation; the large trunk or vessel thatconveys it, branches out, at its entrance into thelungs, into an infinite number of very fine ramifi-cations. The windpipe, which conveys the airfrom the mouth into the lungs, likewise spreadsout into a corresponding number of air vessels,which tollow the same course as the blood vessels,forming millions of very minute air cells. Thesetwo sets of vessels are so interwoven as to form asort of net-w ork, connected into a kipd of spongymass, in which every particle of blood must neces-sarily come in contact with a particle of air.
\
CAROLINE.
But since the blood and the air are contained indifferent vessels, how can they come into contact;
MRS. n.
The}- act on each other through the membranewhich forms the coats of these vessels; for althoughthis membrane prevent* the blood and the air from1