6 ASHBURN AND ORAIG. 



introduced by the bite of D. occidentalis. The location of the bite can 

 not always be determined, possibly because the first symptoms of the 

 fever do not indicate its position as is the case with tsutsugamushi 

 disease. Certainly, an ulcer and lymphadenitis do not always follow. 

 Ricketts's recent observation that nymphal ticks may transmit the 

 disease and his suggestion that larvse may do so, possibly accounts for 

 the absence of a history of tick bite in some cases, as the lesion resulting 

 from the bite of larvse may be so insignificant as possibly to leave no 

 trace after a few hours or a day and the larva itself may be overlooked. 

 The majority of persons in the infected regions carefully watch and 

 examine themselves for tick bites, and it is improbably that the bite 

 of the adult tick is often overlooked. In nearly all cases the disease is 

 contracted on the hill sides or "bench/' high above the river, and some 

 persons long resident in the region say that the bottom lands and islands 

 which are subject to submersion are free from danger. Wilson and 

 Chowning named the disease Piroplasmosis hominis. Later investiga- 

 tions, except that of Anderson, have failed to confirm their view and 

 the disease is not now considered a piroplasmosis. The causative organ- 

 ism is not known. 



A consideration of the etiology of the two diseases shows many points 

 of resemblance, but also some important differences. Both occur in 

 small and usually strictly limited areas along certain streams running 

 through mountainous country. The district in each instance is subject 

 to heavy snowfnll in winter and the streams to spring or summer floods. 

 Along each infected stream the dangerous spots are usually more or 

 less uncultivated and the soil overgrown with underbrush, trees or weeds, 

 while the immune spots are well cultivated. In each country the disease 

 is attributed to the bite of an Acarina, and in each a supposed protozoon 

 blood parasite has been described as its cause, but has not been con- 

 firmed as such. Contagion is unknown in either disease. 



The differences in the etiology of the two infections are equally well 

 marked. The Acarina, the bite of which causes tsutsugamushi, ' is 

 always a six-legged, larval Trombidium, the adult form being unknown. 

 The insect conveying "spotted or tick fever" of Montana is always 

 Dermacentor occidentalis, and usually the adult. Tsutsugamushi disease 

 always occurs after floods, being contracted on ground which has ac- 

 tually been submerged by the swollen river. Fields immediately adjoin- 

 ing the infected areas and but a few feet higher are considered safe. 

 The Montana disease may precede the flooding of the streams or, more 

 usually, accompanies it. It' is very commonly contracted on ground 

 which has not been submerged, but which is on hillsides high above the 

 level of the river. The cases begin in March and rarely appear after 

 the middle of July; tsutsugamushi disease beings to appear in July and 

 continues to occur until some time in October. 



