CLIMA TO LOG Y—MTIOLOGY 



1343 



In 1915 it was noticed at Ismay and Fallow in Montana, which 

 was an extension of its distribution. Possibly it occurs in Alaska. 



It will be noted that these districts extend from 40° to 47° N. 

 latitude, and that the elevation is about 3,000 to 4,000 feet above 

 sea-level, and are sharply defined regions in valleys or at the foot 

 of hills. 



Wilson and Chowning noted that the cases occur from March to 

 July, as is shown by the following list, taken from their report :- — 



March ..... , . . . . . . . 6 casevS 



April . . . . . . . , . . . . 24 ,, 



May . . . . . . . . . . . . . . 46 , , 



June .35 



July 5 



Spring (exact month not known) . . . . 10 



Total . . . . 126 cases. 



This seasonal occurrence is associated, as stated above, with the 

 prevalence of D. under soni during the same months. There is a 

 growing suspicion that there is a difference between the Montana 

 and the Idaho strains of infection. 



etiology. — According to Wilson, Chowning, and Anderson, the 

 cause of the disease is a Piroplasma, but Stiles, x\shburn; and 

 Ricketts have failed to find this parasite. Stiles, Ashburn, and 

 Craig seem to have thought that the disease was due to a 

 trypanosome. If so, this has not been confirmed. The bacterial 

 growths so far obtained from cultures of internal organs or of the 

 blood can be considered as merely accidental contaminations. 



Ricketts has shown that blood taken from a human being suffer- 

 ing from the disease can be inoculated successfully into guinea-pigs 

 and monkeys [Macacus rhesus), and that the transmission from 

 animal to animal can go on apparently indefinitely (100 generations) . 

 These inoculations produce a disease characterized by an incubation, 

 a fever, an eruption, and post-mortem appearances similar to those 

 found in human cases. No bacteria can be cultivated from the 

 internal organs or blood of the infected animals, but the virus exists 

 not merely in the serum, but so closely attached to the corpuscles 

 (white and red) that it cannot be separated from them by washing; 

 moreover, it will not pass through the pores of a Berkefeld filter. 

 Immunity follows an attack, and hyperimmunity can be induced 

 in guinea-pigs. 



Fricks by centrifuging infected serum for four to six hours at 

 2,000 revolutions per minute separated a virulent deposit, in which 

 he found in the serum bright red granular and light blue bodies 

 when stained by Giemsa and in the corpuscles elongated chromatinic 

 bodies. He hesitates to draw any conclusion concerning these 

 bodies, but thinks that the virus multiplies in his cultures. Wolbach 

 finds diplo-bacillary-like bodies, resembling those found by Ricketts, 

 in large numbers in endothelial cells in and around vessels and 

 lymphatics, and in the muscle cells of vessels. He thinks that these 



