536 



ANNALS NEW YORK ACADEMY OF SCIENCES 



low or zero levels of activity. Essentially the same results were ob- 

 tained at doses of 0.2 and 0.25 mg. per kg., except that the survival 

 period was longer. At a dose of 0.1 mg. per kg., the animal survived, 

 although the serum and red cell cholinesterase activities were very low. 

 At 0.02 mg. per kg., the serum cholinesterase activity was reduced to a 

 very low level, 2 per cent of normal, whereas the brain cholinesterase 

 activity was decreased only slightly, to 78 per cent of normal. This 



Table 8 



The Effect of Intravenously Injected Diisoproptl-Fluorophosphate on Mon- 

 key Plasma, Red Cells, and Brain Cholinesterase Activity In Vivo 



marked difference between the decreases of serum and brain cholin- 

 esterase was similar to that obtained at low exposures of monkeys to 

 DFP vapor, and parallels strikingly the in vitro difference in sensitivity 

 between the monkey serum and brain cholinesterases to inhibition by 

 DFP. As will be seen presently, these findings are quite similar to 

 those obtained in man. Although the red blood cell cholinesterase 

 was of about the same order of in vitro sensitivity as the brain cholin- 

 esterase, it was reduced in vivo, at the very low dose, to a greater 

 degree. 



In the monkey, symptoms were absent, even when the serum cholin- 

 esterase levels were zero. In most instances, the occurrence of severe 

 symptoms or death was associated with zero levels of brain cholin- 

 esterase activity. After exposure to, or injection of, DFP, the serum 

 cholinesterase returned very slowly to normal. In the few instances in 

 which this return was followed, about 50 per cent of the normal serum 

 cholinesterase activity was regained in about 7 days. 



Men were also exposed to DFP vapor. One group of 7 men was ex- 

 posed to a concentration of 19 micrograms per liter, for 8% minutes; 



