63 



eradication rests on the removal of undergrowth, the destruction of 

 other mammals (domestic and wild), the destruction of the ticks 

 themselves (principally by means of the lanolin in the wool of the 

 grazing sheep), and the placing of the problem of tick eradication 

 upon an economic basis, so that it may be carried out on an extensive 

 scale without cost. The experiments during 1914 were conducted 

 with 1,500 sheep, and it was estimated that 25,000 adult ticks were 

 destroyed by these sheep during the season, or 50 times the number 

 killed by the regular dipping of all other domestic animals on this 

 ter^ito^}^ The Bitter Root Valley is narrow and flanked on almost 

 ever}^ side by precipitous mountains reaching an elevation of 10,000 

 feet. The ticks and by far the greatest number of small rodents, 

 are found in the foot-hills and along the lower reaches of the mountains. 

 Higher up there are fewer ticks, except around the goat rocks, and 

 fewer small animals to serve as hosts. A large band of sheep started 

 in the foot-liills between two canyons and grazed closely for a week 

 would pick up practically all the ticks in that locality and destroy 

 perhaps 90 per cent, of them ; then by shifting sheep straight back 

 into the mountains to the next camp site, located above the tick 

 zone, the engorged ticks would be dropped where the larvae on hatching 

 would find few suitable hosts. The success of this method rests upon 

 the removal back into the mountains of the sheep with the remaining 

 attached ticks before they are fully engorged and ready to drop off 

 for egg laying, a period which averages somewhat over 10 days from 

 the time of attachment. This appears to have been the exact process 

 by which the ticks were unwittingly eradicated from parts of the east 

 side of the Bitter Root Valley several years ago, when from 30,000 

 to 40,000 sheep were grazed on the lines indicated. The geograph- 

 ical distribution of the disease includes California, Colorado, Idaho, 

 Montana, Nevada, Oregon, Utah, Washington, and Wyoming 

 A bibliography of seven works concludes the article. 



Bacot (A. W.). Observations on the length of time that fleas {Cem- 

 tophyllus fasciatus) carrying Bacillus jjestis in their alimentary 

 canals, are able to survive in the absence of a host and retain the 

 power to re-infect with plague. — Jl. of Hygiene, Cambridge, 

 1st January 1915, Plague Supplement iv, pp. 770-773. 



Cerato'phyllus fasciatus is able to cany Bacillus j^esfis for periods 

 up to 47 days in the absence of any host and subsequently to infect a 

 mouse. Infected fleas, starved for 47 days and then placed upon a 

 mouse, may not infect it for a further period of about 20 days. The 

 positive results of the few experiments made do not necessarily 

 represent the limit of time after which infection may take place, but 

 they indicate that plague infection may persist in fleas for one or two 

 months in cool weather and subsequently give rise to an epizootic. 



Bacot (A, W.). Notes on the development of Bacillus pest is in bugs 

 {Cimex lectularius) and their power to convey infection. — Jl. of 



Hygiene, Cambridge, 1st Januarv 1915, Plague Supplement iv, 

 pp. 777-792, 1 figs., 2 pis. 



• It is concluded that a meal of septicaemic blood from a mouse 

 dying of plague is fatal to a certain percentage of Cimex lectularius and 



