The effect of large doses of X-rays on the resistance of monkeys to experimental poliomyelitis

Abstract

After a few passages through monkeys poliomyelitic virus becomes adapted and virulent for these animals. Hence slight variations in the susceptibility of these animals are not usually observed in experimental work. The original strain adapted to monkeys by Flexner and Lewis has been passed through many monkeys and stored in 50 per cent. glycerol in the ice-box, and its power to infect monkeys is very much diminished. This strain offers the opportunity of detecting variations in the susceptibility of the experimental animal to this infection. In two experiments an intracerebral injection of 1 c.c. of a Berkefeld filtrate of a 5 per cent. suspension of poliomyelitic cord containing the attenuated virus produced typical experimental poliomyelitis in the monkey which has been exposed to large doses of X-rays (6 Holzknecht units daily for six or seven days), whereas in the non-rayed control no symptoms were observed. The doses of X-rays were sufficient to reduce greatly the number of circulating lymphocytes in the blood of the monkeys. In another experiment 0.75 c.c. of the filtrate produced typical experimental poliomyelitis in the X-rayed monkey, whereas 1.0 c.c. produced no symptoms in the control. In an attempt to diminish an active immunity a monkey which had passed through an attack of experimental poliomyelitis and recovered with residual paralysis was exposed to large doses of X-ray so that the circulating lymphocytes were decreased from 27,000 per cu. mm. to about 2,500. TWO separate intracerebral injections of active virus failed to produce any further symptoms or paralyses in this monkey.