No symptoms of DDVP poisoning were observed in any of the rats, monkeys, 
or men during or after exposure in the treated warehouses. 
As shown in table , cholinesterase activity levels for the rats in the 
warehouses. receiving dosages of 1 or 2 grams of DDVP per 1,000 cubic feet 
were not depressed from the control values. However, both male and female 
rats exposed to the 10-gram dosage did show, on the average, some decrease 
of plasma and erythrocyte enzyme action. Figure 1 illustrates the blood 
cholinesterase levels for both plasma and erythrocytes during the period of 
their exposure. The monkeys exposed to the 10—gram dosage showed a more 
severe depletion than did those exposed to the 2-gram dosage. The pre- 
exposure and postexposure plasma and erythrocyte cholinesterase levels of the 
human volunteers are shown in table 5. All l subjects had a decreased plas- 
ma enzyme activity after their first exposure. After the second exposure, l 
person had a further small decrease in plasma cholinesterase, whereas the 
other 3 actually had increased levels, In the erythrocyte enzyme level, 
little change was noted after the first exposure, whereas 3 of the subjects 
had lower levels after the second exposure. These observations were not un- 
expected in view of the known tendency toward rapid recovery of DDVP-inacti- 
vated plasma cholinesterase and the slower recovery rate of the erythrocyte 
enzyme. None of the volunteers at any time showed any severe diminution of 
cholinesterase level, all the variations being almost or completely within 
normal limits of variability for population values, 
A rapid screening test (Limeros-Ranta bromthymol blue method) for the 
determination of approximate cholinesterase levels of the human volunteers 
was carried out at intervals during the tests. None of the individuals, in- 
cluding the ); experimental subjects and 2 controls, showed any decrease in 
cholinesterase level detectable by this procedure (that is, there was less 
than 25 percent decrease). 
Analysis of air samples from the treated warehouses is given in table 6. 
The air in the warehouses treated at dosages of 1 and 2 grams per 1,000 cubic 
feet reached maximum levels of 19.7 and 48.3 milligrams per 1,000 cubic feet, 
(0.7 and 1.7 mmg. per liter) respectively. These values’ decreased to un- 
detectable levels within 8 hours of treatment. In each instance, the maxi- 
mum concentration of DDVP in air actually observed was only about 2 percent 
of the theoretical maximum. The warehouse treated with a 10-gram dosage 
showed about the same DDVP concentration 2) hours after treatment as the one 
receiving the 2=-gram dosage. However, the toxicant concentration remained at 
a high level much longer, still being 11.2 milligrams per 1,000 cubic feet 
after 7 days. 
DISCUSSION 
It is apparent that the vapor phase of DDVP was responsible for most of 
the insecticidal effectiveness demonstrated in these tests. For an insect to 
be affected it was not necessary for it to come in actual contact with par- 
ticles of spray or with the deposit on a sprayed surface. In studies of the 
-lle- 
