658 MICROBIOLOGY OF THE DISEASES OF MAN AND ANIMALS. 



by an invisible microorganism. Blood containing the microorganisms of 

 horse sickness may be kept in sealed bulbs in the dark at room tempera- 

 ture for more than two years without losing its infectiveness. The virus 

 is quite resistant to drying and may survive heating for ten minutes at a 

 temperature of 75. 



INFANTILE PARALYSIS.* 



As indicated by its name, this disease (epidemic poliomyelitis) is usually 

 seen in children. It has long been known to exist in both Europe and 

 America, occurring generally in sporadic form. During the last decade, 

 however, its prevalence has greatly increased and a number of well-defined 

 epidemics have been reported. Though the character of this malady long 

 ago led to the belief that it was caused by a microorganism, this fact was 

 not definitely proven until the year 1909 when Landsteiner and Popper in 

 Germany, and Straus and Huntoon and Flexner and Lewis in the United 

 States, succeeded in transmitting the infection to monkeys. So far as is 

 now known, none of the lower animals except monkeys are susceptible. 



The symptoms and effects of infantile paralysis are extremely variable. 

 Paralysis is by no means constant, many cases being very mild and thus 

 possibly escaping detection. In the severer forms of the disease paralyses 

 of various types and degrees are seen. When recovery takes place the 

 paralysis may appear to improve only to be followed by atrophy of cer- 

 tain groups of muscles, resulting in deformity and permanent lameness. 

 These effects are caused by the destruction of certain nerve centers in the 

 spinal cord. 



As stated above, the microbial origin of infantile paralysis was first 

 demonstrated by the inoculation of monkeys, Flexner and Lewis having 

 successfully carried the infection through a long series of monkeys by 

 successive intracranial injections of an emulsion of the spinal cord taken 

 from infected animals. The microorganism passes through the Chamber- 

 land and Berkefeld filters with little or no loss in disease-producing power. 

 It has never been cultivated artificially nor recognized under the micro- 

 scope. The virus withstands freezing or drying for long periods of time 

 but is quickly destroyed by heating at a temperature of 50. It is likewise 

 quickly killed by the ordinary disinfectants. Monkeys may be infected 

 by the subcutaneous, intraperitoneal, intravenous, or intracranial injection 



* Prepared by M. Dorset. 



