51 
warm countries does not allow us to suppose that the day- 
light always, produces in vapours an innocent state, although 
it has a great effect in that direction when there is little 
O 
water.” M. Duclaux evaporated cultures of microbia in 
tubes, and then preserved the dried spores, carefully pro- 
tected from external contamination, some being sheltered 
from the sun-light, and others being exposed to it, for 
various periods. The temperature of the sheltered tubes 
was regulated in all cases so as to be approximate to the 
maximum heat obtained from the sun by the exposed tubes, 
so that, excepting the light rays, the conditions in all cases 
were equal. On suitable infusions for culture being sub- 
sequently added, M. Duclaux found that the sheltered spores 
developed much more readily and abundantly than the 
exposed spores ; the sun-lit tubes proved, in fact, more or 
less sterile, according to the time of exposure, those which 
were exposed for the longest time entirely failing to give 
any evidence of microbe life. The fermentive action of the 
specific microbe experimented with, Tyrothrix scaber, is 
analogous to that of pathogenic microbia, as it destroys 
albuminoid matter ; though it is important to bear in mind 
that it is what M. Pasteur calls an aerobic species. The 
dried spores of this microbe, when protected from the direct 
light rays of the sun, resisted the action of free air and a 
tropical temperature for three years, and germinated at the 
end of that period. A month’s exposure to the sun-light, 
however, diminished the germinating power of the spores, 
and after two months’ exposure 50 per cent, of the tubes 
proved sterile. Similar experiments were tried with patho- 
genic micrococci. Cultures in broth preserved their vitality 
for at least twelve months, if sheltered from the direct rays 
of the sun. Exposure for forty days to the feeble and inter- 
mittent rays of the spring killed them; a fortnight’s ex- 
posure to the July sun killed them ; and exposure for a less 
number of days attenuated them and deprived them of all 
