80 
ENOS WALTER. 
therefore purely functional in its character, it is rare for it to 
continue for any great length of time without causing some 
organic affection of the lungs or heart. The most common 
sequel of asthma is emphysema. 
“ The cause of this emphysema is seen in the fact that when 
the inspiratory muscles act they tend, by the negative pres¬ 
sure which they exert on the contents of the thorax, to dilate 
not only the air-cells but also the tubes leading to them ; while 
the positive pressure exerted by the expiratory muscles tends 
to close the already partly closed bronchioles at the same 
time it is trying to force air out through them. Hence air 
can enter the lungs much more easily than it can escape, and 
after each respiration a larger quantity of residual air remains 
in the lungs till the positive pressure exerted by the elasticity 
of the lung tissue, added to that exerted by the muscles of ex¬ 
piration, is sufficient to expel as much air as the inspiratory 
muscles can bring in. 
“ Owing to this same negative pressure, or tendency to pro¬ 
duce a vacuum, the capillary blood vessels of the lungs be¬ 
come distended and congested. Frequent and severe attacks 
in time cause this dilatation to assume a permanency, and 
chronic congestion is the result. This state of chronic con¬ 
gestion is occasionally attended with serious exudation into 
the interalveolar tissue, which, by pressing upon the adjacent 
air-cells causes their obliteration. This oedema with the re¬ 
mains of the compressed air-cells and the viscid mucous stag¬ 
nation in the finer tubes, forms the little islets of carnified 
tissue known as lobar pneumonia. 
“ Hypertrophy of the muscular walls of the bronchial tubes 
is also seen in old cases of asthma ; this thickening of their 
walls causes diminished calibre. 
“Among human beings there are two asthmatic males to 
one asthmatic female. There is no case recorded of the death 
of a human being from uncomplicated asthma. 
“ Causes of asthma in people: 
“ Enlarged bronchial glands pressing upon the pneumogas- 
tnc nerves may cause it. In the great majority of cases, 
however, the exciting cause does not act directly on the pneu- 
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