BROKEN WIND. 
79 
Now let us bear in mind these points: 
1. The elasticity of healthy lung tissue is equal to a force 
of 72 pounds per square foot of lung surface, which is suffi¬ 
cient to expel air from the lungs without aid from the expira¬ 
tory muscles, while the animal is in a state of repose. 
Also that the movements of the lungs are entirely passive. 
2. The respiratory center may be stimulated by lack of 
oxygen in the blood supplied it, and also through the action 
of sensory nerves which are irritated by excess of carbon di¬ 
oxide or lack of oxygen. 
3. Disease often begets an irritable condition of -parts 
affected, and this irritable condition of nerves tends to make 
them magnify impressions—or in other words makes them 
over-sensitive. 
1 4. The vagus is a stimulating nerve to the respiratory cen¬ 
ter, and also by its action causes contraction of the bronchial 
tubes. 
I beg leave to present here a few points on asthma in man 
which I quote from Pepper’s “ System of Medicine.” 
i “ Asthma is a violent form of paroxysmal dyspnoea, not 
dependent upon structural lesion ; characterized by wheezing 
respiration with great prolongation of the expiration and the 
absence of all symptons of the disease in the intervals of the 
attacks. 
“ In ordinary respiration the inspiratory movement is twice 
as long as the expirmm. In asthma this is reversed, the expi¬ 
ratory movement being four or five times as long as the 
inspirium. 
“ The wheezing sound is usually heard only during expira¬ 
tion. 
“ Although the dyspnoea is great, there is no increase in the 
frequency of the respirations so long as the patient lemains 
quiet, but on the contrary they are often less frequent than in 
health. 
“ The circumference of the chest is increased during the 
paroxysm, due to transitory emphysema, which disappears 
with the attack. 
“ Although bronchial asthma is essentially a neurosis and 
