18 
F. S. BILLINGS. 
condition of the lungs by uhich the alveolae do not contain any air , 
or in the place of the air any other elements whatever ; in other 
words , they contain nothing , are collapsed , non-distended . The 
lungs of the foetus exemplify this condition, and we therefore 
name the foetal condition (Etat foetal, Legendre.) of the lungs a 
natural atelectasis . 
The aim of respiration is to convey the oxygen of the air 
to the blood, and to take up from the same the end pro¬ 
ducts of the processes of oxydation, especially the carbonic acid, 
and give them up to the external atmosphere. The lungs are in 
connection with the external world by means of the bronchi, the 
trachea, the larynx, and the nasal cavities. We must then look 
upon these parts as the respiration’s way, the connective-tube 
between the lungs and the atmospheric air. From this considera¬ 
tion it results that the diameter of this respiratory-way decides 
how much atmosphere may gain access to the lungs with each 
respiration. The results of different measurements indicates that 
the diameter of this connective-tube stands in a certain relation 
to the size of the lungs, and that the size of lungs stands in a cer¬ 
tain relation to the size of the body. 
To the completion of normal respiration, a normal diameter of 
the respiratory-tube is necessary, and every considerable constric¬ 
tion of the same must necessarily produce a disturbance in the 
execution of the respiratory functions. When this connective- 
tube is obstructed, the entrance of the air into the lungs cannot 
take place. Such a condition may take place during the birth of 
the young animal. The young are forced out by the contraction of 
the uterus, but at first the uterus does not act upon the foetus, but 
upon the liquor amnii. The orificium uteri is distended by that 
part of the foetal meninges which obstetricians designate as the 
“ blase 71 bladder. Later, the head of the foetus is pushed into the 
distended orificium, and finally the foetus is born. The young, 
while intra-uteral, draws its necessary oxygen from the placental 
blood of the mother, but this gaseous-exchange between the blood 
of the young and that of the mother is only possible when the 
way by which the blood passes from the mother to the foetus, and 
vice versa , is unobstructed. As soon as the young is born, also 
