496 INFECTION AND RESISTANCE 



Health, in 1917, on the basis of the work done during the great 

 epidemic of 1916. 



Seasonably the disease has almost invariably been one of hot 

 weather. There are a few exceptions to this, one of them a great 

 epidemic in Sweden in 1911, which was at its height from October 

 to December. Some others have begun as early as March. 



Formerly the disease was regarded as chiefly rural, but of late 

 years it has also extensively prevailed in cities. 



The age incidence is important, in that the majority of cases 

 (about 90 per cent) have occurred in infants under ten, although a 

 few epidemics among adults have been observed and a few adult cases 

 always accompany epidemics. In other people the disease often 

 takes the form of what was formerly known as Landry 's paralysis. 

 Indeed, in a little epidemic which we studied in Palo Alto, Cal., 

 the first cases which died were adults, with typical Landry symp- 

 toms; and successful monkey inoculation was made from a woman 

 of 26 whose symptoms were those of a typical Landry paralysis. 



Relation to domestic animals has often been suggested, and 

 Frost (U. 8. Hygienic Laboratory Bulletin 90, 1916), who studied 

 this extensively during the last epidemic, made careful observations 

 on this factor, finding that there is no demonstrable relationship. 

 The diseases of dogs and chickens investigated by others, which 

 simulated the human disease, have been found to be due to distinct 

 pathological conditions without any relationship to human poliomye- 

 litis. A paralytic disease of cats occurring in New York during the 

 last poliomyelitis epidemic was studied in our laboratory by Dr. 

 Messing and found to have been caused by a Gram negative bacillus. 



Because of the seasonable occurrence insects were long suspected 

 as possible carriers, and M. J. Rosenau a few years ago carried out 

 experiments in a few of which he succeeded in infecting monkeys 

 by the bites of stable flies (Stomoxys) which had been fed on the 

 virus. There has been but a single confirmation of this by Ander- 

 son, and all other attempts to confirm Rosenau' s observation have 

 been negative. Investigations of other flies, or bed-bugs, fleas, mos- 

 quitoes, etc., have invariably been negative. While therefore stable 

 fly transmission cannot be accepted as a common method of infec- 

 tion, and probably plays no practical role whatever, we must bear 

 in mind that there have been two successful experiments in the work 

 of two reliable and skilled experimenters, and should be alert for 

 further evidence in this direction. 



Important positive knowledge concerning the transmission of 

 the disease is that which has been gained by the investigations of so- 

 called "carriers." It has been found both in monkeys and human 

 beings that the virus of the disease can be carried in the upper 

 respiratory passages of convalescents for as long as months after 

 recovery. It has also been found in a single instance that a monkey 



