PATHOLOGY OF PULMONARY DISEASES OF THE HORSE. 
23 
lungs, and then the latter becomes atelectatic. The question now 
before us is : How does the excluded part of the lungs get freed 
from its air ? Here works the repeatedly quoted elasticity of the 
pulmonary tissues. The air in the excluded parts of the lungs 
finds itself under a constant pressure, and this conditions the 
absorption of the air. 
Virchow was the first to advocate the view, that the air in the 
excluded parts of the lungs was absorbed by the fluid present in 
the same. This absorption process takes place here in the same 
manner as in the intestines. The absorbed air gains access to the 
blood, and is rapidly passed off by means of the lungs, as Bernard 
has shown. According to Traulee, nitrogen is not easily absorbed 
by the blood, and it appears as if the nitrogen in the intestines 
gained access to the blood easier through the mucosa of the same 
than by serous membrane, that is, the lungs. Investigations have 
shown that the air in such excluded parts of the lungs is at first 
always poorer in oxygen and richer in carbonic acid, and that 
then comes a period when only carbonic acid and nitrogen are to 
be found in the parts in question, and that finally these gases also 
become absorbed, the carbonic acid quicker than the nitrogen, 
however. The tonus of the tissue is one of the most important 
conditions for the absorption of the gases. Opposed to the tonus 
is the atonus, and both conditions are dependent upon the inner 
construction of the tissues. Authors, in times past, have desig¬ 
nated these conditions of the tissues with “ strictum 55 and 
“ laxum.” Tonus has reference to the dense and firm condition 
of well nourished parts. Tonus, says Virchow, is the character 
of a healthy, normal part, where the favorable condition bespeaks 
also a large amount of activity. The property of a part to retract 
itself, is known as its elasticity. Pulmonary tissue is able to 
retract itself, when in a good condition, powerfully and quickly > 
under the contrary circumstances, slowly and imperfectly. The 
lungs may lose their capability to retract; in such a case we speak 
of a collapsus of the lungs. From this it is evident that atalectasis 
of the lungs must not be confounded with collajpsus. A lung can 
only become atelectatic vjhen it has the ability to retract itself \ that 
is, when it is elastic; it is only parts which have this ability which 
