SURGERY

approximately three grsmmes of parathion together with small amounts of its isomers, paraoxon and p-nitrophenol, per square metre. The strips are sold in hermetically sealed containers with a label stating that protective gloves must be worn when the strips are handled while being suspended under the roof in stables and cow-sheds; the strips are not to be used in houses; the strips are poisonous to humans and animals; and -containera and strips should be destroyed immediately after use. The field investigation showed that the use of the strips in cow-sheds did not affect the cholinesterase activity of erythrocytes or plasma in the farmworkers concerned over a period of a month. Laboratory experiments with guinea-pigs exposed to parathion-impregnated gauze strips at temperatures of 25° C. and above, and with a ventilation below 2·5 air changes per hour, showed that under these adverse conditions the plasma cholinesterase .activity was reduced. Erythrocyte cholinesterase activity, which is small in guinea-pigs, was not estimated. The reduction in plasma cholinesterase activity was stabilized after seven to 14 days' exposure.