20 
J*- ~ / * 
F. 8. BILLING-S. 
following muscles taking especial part in this phenomena, viz : 
the diaphragma, the scaleni, the inter-costales externi and interni. 
Expiration takes place without the interposition of muscular 
force ; the most essential expiratory force being the elasticity of 
the pulmonic tissues themselves. The inspiration’s muscles relax, 
and the lungs which have been distended have, on account of 
their own elasticity, the tendency (endeavor) to again assume the 
volume they had at the time of the last completed expiration. 
While the elasticity is a hindrance to the inspiratory extension of 
the lungs, it is the chief motor in the performance of the expi¬ 
ratory act. The endeavor of the lungs to contract themselves, 
has not by any means ended with the termination of the expira¬ 
tion, as we shall presently see. 
As the inspiration is affected only by means of muscular force, 
it must then essentially depend on the condition of the muscles 
for inspiration, whether on coming into the world the young ani¬ 
mal can sufficiently widen the individual sections of its thorax or 
not. Unfortunately , we do not at present possess any satisfac¬ 
tory 'measurements of the excursions of the single sections of the 
thorax. Experience has, however, taught us that sections of the 
lungs, of more or less extent, remain in a foetal, that is atelectatic, 
condition, when the inspiration’s muscles do not sufficiently work 
after the birth of the young; that is, all parts of the lungs are not 
equally extended. 
Roloff found by young pigs immediately after birth, and even 
by not yet developed foetus, the entire straited musculature in a 
condition of fatty metamorphoses; consequently in a condition 
unsuitable to perform its functions. These animals could only 
inspire imperfectly, or not at all. Many animals therefore per¬ 
ished at once, or soon after birth, in consequence of insufficient 
respiration. The lungs of the dead animals appeared, as a rule, 
in desiccated atelectatic condition, (“ in der Hegel trocken.”) 
The lungs will then remain in a foetal condition: 1st. When the 
inspiration muscles have suffered patliic metamorphosis, and every 
extension of the thorax is impossible; or, 2d. When the respira¬ 
tory tract, the connective-tube between the lungs and the exter¬ 
nal air, is obstructed. The nature of the changes of the inspira- 
