li'li'I Han-is-lloijl: Aclioii of I'llrariolcl Lif/lit on Barleria 247 
ineubated twcjily-iuur lioiuvs, and tliu colonics were identified 
directly, or, in siispicioiLs eases, smears were made. The objection 
to this method was that there was no certainty tliat the control 
streak and the exposed streak were similarly inoevdated. 
/;. To overcome this objection a single large streak in the shai)e 
of the letter "Z" was made of one loopfnl of bacterial suspension, 
and half the plate exposed as before. 
(■. Another plating method experimented with was to flood 
the entire plate with a definite amount of saline suspension and 
then expose one side, as in the above. 
Plating methods were also abandoned finally because they did 
not yield uniform results, due undoubtedly to some oi-ganisms 
getting in under the agar and being protected by the protein 
material. 
The method finally employed was a cover slip method suggested 
by Professor Ivan C. Hall. Upon one .surface of a sterile cover 
.slip one loopful of saline suspension of a twenty-four hour agar 
growth was placed and allowed to dry in a sterili> peti'i dish. 
Assuming the saline suspension to be uniform each cover slip 
therefore had approximately the same number of organisms. 
When dry the cover slips were exposed directly to the rays by 
placing them in a petri di.sh 12 cm. below the arc of the Cooper- 
Hewitt machine. After the given exposure the cover slip was 
picked up with sterile forceps, dropped into a tube of broth, 
the broth was incubated for forty-eight hours, and the results 
observed. The growth of these three organisms in broth is quite 
characteristic, and no further examination was usually necessary. 
In doubtful eases agar plates were streaked from the broth and 
the organisms were identified by the usual methods. 
The exposures varied from five seconds to 200 seconds. Some- 
what over 100 exposures were made, and although there were 
slight discrepancies in the results, due to the objections mentioned 
to plating methods, consistent results were obtained by the cover 
slip method, so that we may definitely say that : 
Bacillus mucosus capsulatus was killed after 20 seconds. 
Staphylococcus " " " 90 " 
B. suhtilis " " "150 " 
