SiGERSON — On the Atmosphere. 
29 
the disease. The indication would rather seem to be to cleanse the lungs 
by inducing a mucous discharge. 
Secondly — That the lungs have a power, not hitherto suspected, of 
absorbing or assimilating even solid matter. It is clear from what 
I stated of Pouchet's anatomical discovery of objects in the air pipes, 
as well as from Professor Tyndall's experiments, that a considerable 
quantity of matter frequently and generally remains in the lungs. 
Some may be got rid of by mucous discharges ; but evidently all is 
not thus usually expelled. Some of the carbon and iron in the iron 
factory dust no doubt remain ; and, unless the lung is to be clogged up, 
it must dispose of them somehow by absorption. Old lungs get a grey 
colour from the dust they absorb. It does not appear more difficult 
for the lungs to do this thing, than for the delicate fibrillae of the roots 
to accomplish it. It may be remarked that carbonic dioxide acts as a 
solvent in many cases, and that in the lungs are carbonic dioxide, 
oxygen, and moisture, all which favour the dissolving act. 
Thirdly — That the theory of panspermism seems unfounded on fact — 
that there are no hosts of germs always floating about in the atmo- 
sphere, invisible and maleficent as genii of Eastern stories. Air is not 
much better, but not generally worse than water. Professor Tyndall 
has set the sunbeam prominently before us ; but I have come upon 
atmospheres where a sunbeam could not be seen, for want of motes. 
Within doors at a country place, in winter, the motes were plenty, and 
the sunbeam well defined ; out of doors, in a calm spot, I could see 
the bright slit where the ray entered the bower : I could see the 
white spot on the floor where it fell, but between these two visible 
points there was no visible line. It was impossible to say where the 
ray was, until the hand was placed in its way, or a little dust shaken 
through it. The dust produced patches of visible light in this invisible 
ray, just as Professor Tyndall caused patches of stellar darkness by ex- 
pelling dust out of his visible ray. This fact will, I hope, satisfy the 
talented editor of " Scientific Opinion," that Professor Tyndall's ex- 
planation was correct, and that conditions of polarization need not to be 
sought for. 
Fourthly- — The germ theory" asserts, That epidemic diseases are 
due to germs which float in the atmosphere, enter the body, and pro- 
duce disturbance by the development within the body of parasitic 
life."'^ This is stated to be opposed to the opinion that epidemic diseases 
are ' ' propagated by a kind of malaria, which consists of organic matter 
in a state of motor decay. ''^ ]^ow, for my part, I object to the claim of 
monopoly here set up. There is no necessary opposition ; the action 
of one agency does not here exclude the action of another agency. 
There may be constitutional disturbance produced, both by the growth 
of spores and action of mucus particles. 
The germ theory" is supposed to be supported by the so-called fact, 
that putrefaction is caused by germs derived from the air, which 
* Professor Tyndall's Lecture on Dust and Disease. 
