July 21, 1916] 



SCIENCE 



75 



keys enter through the intestines. But 

 while the latter two modes of infection may 

 operate sometimes, observations upon hu- 

 man eases of infantile paralysis and upon 

 animals all indicate that the main avenue 

 of entrance of the virus into the body is by 

 way of the upper respiratory mucous mem- 

 brane — that is, the membrane of the nose 

 and throat. 



Besistance of the Virus 

 The physical properties of the virus of 

 infantile paralysis adapt it well for con- 

 veyance to the nose and throat. Being con- 

 tained in their secretions, it is readily dis- 

 tributed by coughing, sneezing, kissing, and 

 by means of fingers and articles contami- 

 nated with these secretions, as well as with 

 the intestinal discharges. Moreover, as the 

 virus is thrown off from the body mingled 

 with the secretions, it withstands for a long 

 time even the highest summer tempera- 

 tures, complete drying, and even the action 

 of weak chemicals, such as glycerin and 

 carbolic acid, which destroy ordinary bac- 

 teria. Hence mere drying of the secretions 

 is no protection; on the contrary as the 

 dried secretions may be converted into dust 

 which is breathed into the nose and throat, 

 they become a potential source of infection. 

 The survival of the virus in the secretions is 

 favored by weak daylight and darkness, and 

 hindered by bright daylight and sunshine. 

 It . is readily destroyed by exposure to 

 sunlight. 



Conveyance by Insects 



Since epidemics of infantile paralysis al- 

 ways arise during the period of warm or 

 summer weather, they have been thought of 

 as possibly being connected with or depend- 

 ent on insect life. The blood-sucking in- 

 sects have especially come under suspicion. 

 Experiments have been made with biting 

 flies, bed-bugs, mosquitoes, and with lice. 

 Neither mosquitoes nor lice seem able to 



take the virus from the blood of infected 

 monkeys or to retain it for a time in a living 

 state. In one instance, bed-bugs have been 

 made to take up the virus from the blood 

 of monkeys, but they did not convey it by 

 biting to healthy monkeys. Certain experi- 

 ments did indicate that the biting stable 

 fly could both withdraw the virus from the 

 blood of infected and reconvey it to the 

 blood of healthy monkeys, which became 

 paralyzed. But more recent studies have 

 failed to confirm the earlier ones. More- 

 over, experimentally inoculated monkeys 

 differ in one way from human beings suf- 

 fering from infantile paralysis, for while 

 the virus may appear in the blood of the 

 former, it has never been detected in the 

 blood of the latter. The ordinary or domes- 

 tic fly may become contaminated with the 

 virus contained in the secretions of the body 

 and serve as the agent of its transporta- 

 tion to persons and to food with which they 

 come into contact. Domestic flies experi- 

 mentally contaminated with the virus re- 

 main infective for 48 hours or longer. 

 While our present knowledge excludes in- 

 sects from being active agents in the dis- 

 semination of infantile paralysis, they 

 nevertheless fall under suspicion as being 

 potential mechanical carriers of the virus 

 of that disease. 



Conveyance by Domestic Animals 

 The attention which the recent epidemic 

 of infantile paralysis has drawn to the dis- 

 eases attended by paralysis has led to the 

 discovery that domestic animals and pets 

 are subject to paralytic diseases. The ani- 

 mals which have especially come under sus- 

 picion as possibly distributing the germ 

 of infantile paralysis are poultry, pigs, 

 dogs, and eats. But in isolated instances, 

 sheep, cattle, and even horses have been 

 suspected. All these kinds of animals are 

 subject to diseases in which paralysis of the 

 legs and other parts of the body sometimes 



