1885.] 
Sanitary Agency of Light. 
595 
in his observations. But he— in our opinion very iudi- 
to°whfch mk'mh- 11 WeU t0 remain in the normal conditions 
o microbic germs are exposed when suspended in 
d /P 0Slted , 0 ? the surfaces of various bodies It is 
to be hoped nevertheless, that a second series of researches 
Sh°tTln f °^ ll° w , to ascertain the influence upon these beings 
whirl V ^ aS ^t 111 ? 111811601 heat. The only condition 
fhr trm aS b f Cn ohse f ve . d as re gards heat was not to exceed 
tie temperatures which have been found most suitable for 
en cultivation, and which lie between 86° and 104° F. 
The temperature in the sun sometimes rose much higher.’ 
he limits of vitality which M. Duclaux found in his expe- 
nments are therefore maximum limits, and are so especially 
under the influence of the solar light. y 
The results may be briefly summarised as follows : — 
Young cultures of the micrococci in neutralised veal broth 
which live on an average more than a year if kept in the 
dark or in diffused light, only resisted this year the feeble 
and intermittent sunshine of the spring for forty days, — that 
is, from May 4th to June 13th. In July fifteen days of ex- 
posure were sufficient to kill them, and a shorter time 
sufficed to attenuate them and to deprive them of all aftion 
upon the organism even of those animals which are most 
susceptible to their influence. 
The vitality is still feebler if a micrococcus is preserved in 
the diy state, in the imperceptible coating which is left by a 
drop of culture liquid evaporated on the bottom of a flask 
1 he micrococcus of the “ Biskratt boil ” and that of Pem- 
phigus, which were found still living after being kept for five 
to six months in this dry condition in the dark, have been 
killed by eight days’ exposure to the sun, from May 26th to 
June 3rd. In July two to three days were sufficient, and it 
was about the same for other species. None of those which 
M. Duclaux studied resisted three days of insolation, from 
July 7th to 9th, at a window facing the south, but which 
received the sun only for four hours daily, from 9 a.m. to 
1 p.m., and where the temperature never exceeded 102° F. 
These are lower figures than those which the same biolo- 
gist has previously found for bacilli. The difference probably 
turns on the fadt that in the micrococci the most resistant 
state of these beings, if it exists at all, is rare and still 
unknown. 
But however this may be, it is interesting to establish the 
fa (ft that a few hours of exposure to the sun suffice first to 
attenuate and finally to kill these micrococci, which include 
so many formidable and widely distributed species, It thus 
