576 DISEASES OF UNKNOWN ETIOLOGY 



reaches maturity usually within four to six days in place of seven to 

 ten days. Less commonly an "immediate" reaction is met with; 

 the site of inoculation becomes reddened and the lesion is greatest 

 within twenty-four hours after the inoculation. The reddened area 

 fades rapidly and the entire process heals almost as quickly as the 

 simple reaction of trauma excited by the scratch in the epidermis. 

 The accelerated and immediate reactions are usually regarded as 

 potentially equivalent to a typical reaction, provided they' are induced 

 by re vaccination. 



Dengue.- r The etiology of dengue has not been definitely estab- 

 lished, but it appears to belong to the group of filterable viruses and 

 to be transmitted by Culex fatigans, a mosquito very common in the 

 tropics. Graham 1 claimed to have transmitted the disease to non- 

 immune individuals not only through the bite of infected female 

 Culices, but also by injecting the ground up salivary glands of a mos- 

 quito that had previously bitten a patient. Ashburn and Craig 2 

 state that the virus will pass a Berkefeld filter and that both whole 

 blood and serum filtered through Berkefeld filters will reproduce the 

 disease in non-immune individuals. The incubation period in these 

 cases was about four days. Ashburn and Craig believe with Graham 

 that the virus of dengue is ordinarily transmitted by Culex fatigans. 



Rocky Mountain Spotted Fever. Rocky Mountain Spotted Fever 

 is an acute fever characterized by a purpuric eruption of the skin. 

 The disease is rather strictly limited to the Northern Rocky Mountain 

 States, Montana, Wyoming and Idaho. 



The etiological agent is not definitely known. Wilson and Chown- 

 ing 3 believed the causative agent to be a Babesia transmissible by a 

 tick, Dermacentor reticularis (now known as Dermacentor occiden- 

 talis). This view was not supported by later observers. Ricketts 4 

 in numerous investigations has shown that the virus circulates in the 

 blood stream, and that infected ticks may transmit the disease. He 

 was also successful in infecting monkeys (Macacus rhesus) and guinea- 

 pigs with the virus. One attack conferred immunity to subsequent 

 infection in experimental animals, and the serum of an immune 

 animal protected a susceptible animal from infection. As a curative 

 agent the serum was of little value. A minute diplococcoid or bipolar 



1 Jour. Trop. Med., 1903, vi, 209. 



2 Philippine Jour. Sci., 1907, ii, 93. 



3 Jour. Inf. Dis., 1904, i, 31. 



4 Jour. Am. Med. Assn., 1906, xlvii, 33, 358; 1907, xlix, 24, 1278; Trans. Chicago 

 Path, Soc., 1907; Jour. Inf. Dis., 1908, v, 221; Jour. Am. Med. Assn., 1909, lii, 379. 



