RELATIONS. 
149 
passage, which might carry on the communication requir¬ 
ed, until the other was open. Now this is the thing which 
is actually done in the heart: instead of the circuitous route 
through the lungs, which the blood afterwards takes before 
it gets from one auricle of the heprt to the other, a portion 
of the blood passes immediately from the right auricle to 
the left, through a hole placed in the partition which sepa¬ 
rates these cavities. This hole anatomists call the fora¬ 
men ovale. There is likewise another cross cut, answering 
the same purpose, by what is called the ductus arteriosus, 
lying between the pulmonary artery and the aorta. But 
both expedients are so strictly temporary, that after birth 
the one passage is closed, and the tube which forms the 
other shrivelled up into a ligament. If this be not contri¬ 
vance, what is? 
But, forasmuch as the action of the air upon the blood 
in the lungs appears to be necessary to the perfect concoc¬ 
tion of that fluid, i. e. to the life and health of the animal, 
(otherwise the shortest rout might still be the best,) how 
comes it to pass that the foetus lives, and grows, and thrives, 
without it? The answer is, that the blood of the foetus 
is the mother’s; that it has undergone that action in her 
.labit; that one pair of lungs serves for both. When the 
animals are separated, a new necessity arises; and to meet 
this necessity as soon as it occurs, an organization is pre¬ 
pared. It is ready for its purpose; it only waits for the 
atmosphere; it begins to play the moment the air is admit¬ 
ted to it. 
CHAPTER XY. 
RELATIONS. 
When several different parts contribute to one effect; 
or, which is the same thing, when an effect is produced 
by the joint action of different instruments; the fitness of 
such parts or instruments to one another, for the purpose of 
producing, by their united action, the effect, is what I call 
relation; and wherever this is observed in the works of 
nature or of man, it appears to me to carry along with it 
decisive evidence of understanding, intention, art. In 
examining, for instance, the several parts of a watch, the 
spring, the barrel, the chain, the fusee, the balance,. the 
wheels of various sizes, forms, and positions, what is it 
N* 
