Comments Re. Dr. Lederberg's Questions
Cronar is a selected grade of mylar.

Mylar is a polyester film - made of polyethylene terephthalate -
the polymer formed by the condensation reaction between ethylene
glycal and terephthalic acid.

The specific film which we are using is DuPont Type POA "Cronar"
plain motion picture leader, 16 mm wide, and perforated on two sides.

The material has an anti-static treatment on om side.

As we use the film, only one side is satisfactory for our purposes.
To determine which side is "good" we apply the ethyl violet stain to
both surfaces; the side that does not take up the stain is the side on
which we impact our sample,

Re. the Selection of Ethyl Violet

This dye was selected empirically. Our first thought was to
detect the bacteria by their UV absorbing properties. This fizzled
when we noted that the absorbancy at 265 mam decreased quite sharply as
the organism aged. A 1j~18 hr. culture showed quite weak absorption
of UV.

The next step was to look for a UV absorbing dye which would
"enhance" the absorption of UV by the organism. After studying about
hO dyes, safranin-O0 seemed most promising.

Then we looked at the visible spectrum. A study of 63 dyes showed
ethyl violet to be the best. (Acid fuchsin is best for spores). Since
the ethyl violet was better than the UV absorbing safranin-0, we chose
the former.

SOL NELSON