August, '12] BRUES AXD SHEPPARD: IXFAXTILE PARALYSIS 315 



of the disease for the falhng off of poUomyeHtis in winter is far more 

 noticeable than the lessened abundance of fleas. Also, fleas would 

 tend to distribute the disease more generally throughout families than 

 actually occurs, although they mi^ht, of course, account for its carriage 

 to considerable distances through the migration of animals to which 

 they might be attached. 



It seems probable, therefore, that fleas plaj- no role in the trans- 

 mission of poliomyelitis. 



There remains onh' one other important group of insect -like animals, 

 the ticks or Acarina, which must be considered, as some of these have 

 been shown to be specific carriers of several diseases both of man and 

 domestic animals. 



At the beginning of the present investigation it was suspected that 

 ticks might quite likely be associated with the spread of acute epi- 

 demic poliomyelitis, and an attempt was made to determine the pres- 

 ence of these in the immediate environment of all the cases. It was 

 also ascertained with as gieat accuracy as possible whether ths patient 

 had actually been bitten b}' these animals, or whether it could reason- 

 ably be supposed that he might have been. As the work progressed, 

 it became increasingly difficult to formulate such a theory in accord- 

 ance with the observed facts, however, and it had to be abandoned for 

 the present. Nevertheless, one peculiarity has been observed in the 

 recurrence of the disease in epidemic form which appears inexplicable 

 on any other basis: there seems to be a well-marked tendency for a 

 region where acute epidemic poliomyelitis has been abundant one 

 season, to be comparatively free from the disease the following year 

 but to show a well-defined epidemic the second season. Such a recur- 

 rence every other year is not always very pronounced, but is still 

 noticeable, and if this is the expression of factors involved in the spread 

 of the disease, seems to find no explanation except on the basis of 

 infection carried by some insect which requires two years to mature. 

 The commonest tick met with on domesticated animals in Massa- 

 chusetts is Amblyomma americanum, and according to Bishopp^ this 

 tick usually requires two years to attain maturity' in this region. It 

 rarely affects man, and could thus hardly- be the primary cause of 

 human cases, even had we not failed to demonstrate its presence com- 

 monly about cases this summer. Several assumptions are therefore 

 necessary to associate it with acute epidemic poliomyelitis, and, 

 although these involve the matter in such great doubt, it seems worth 

 while to outline briefly what these are: 



1. That human cases are the result of infection from animals, at 



> /n ZiL, Sept. 20, 1911. 



