LIVE POLIO IRUS VACCINES

62
Safety-Laboratory Evidence of Attenuation and Safety
__
Log. 1 0
PFU/ml.
-8 , _
40 ° C.
37 ° C.
MAH
-6 'L
-4 '
-- ?_ C- L¿
2 6 10 Hrs.
FIG. 2
TABLE 13. COMPARATIVE INFECTIVITY OF INTACT VIRUS AND INFECTIOUS RIBONUCLEIC ACID FOR
THE MS AND MK CELLS
VIRUS INOCULUM RATIO OF TCD50 OF MS TO MK
CHAT INTACT VIRUS 1 : 6
RNA 3.3: 1
MAHONEY INTACT VIRUS 3 : 1
RNA 3.7 : 1
the system used by Holland, where infectious
nucleic acid will yield intact virus non-infectious
for the cell system into which it was introduced.
Similar results were obtained when intact CHAT
virus was used to infect MS cells in the presence
of deuterium oxide (heavy water) in the medium.
Substitution of hydrogen by deuterium in
]iving systems has been studied for some time in
various laboratories and has been found to have
distinetive biologic effects. In the field of virus
infections, the burst size of T7 bacteriophage
was increased when the phase was permitted to
multiply in E. coli grown in D 2 0 medium instead
of H 2 0 medium. The data presented in
Table 14 seem to indicate that the plating efficiency
of CHAT virus on MS cells grown in