102 



use in cattle dips, and of developing some method that may easily 

 be carried out for freeing fields and farms from the cattle tick. A 

 map is given showing the boundary line of the infected area at the 

 beginning of the tick eradication operations in 1906, and the extent 

 to which the area has since decreased. Above the latitude where 

 the cattle tick is destroyed by the cold of winter, the disease can be 

 controlled by keeping southern tick-infested cattle from passing 

 through the country during certain seasons. 



After leaving the host, the female tick may lie quietly on the ground 

 for several days before depositing its eggs. Oviposition may be spread 

 over a period of 4-8 days in summer and 2 weeks or even longer in the 

 autumn. A mature female will lay 1,500-3,000 eggs, and the imma- 

 ture females also lay eggs, but in smaller numbers. The female soon 

 dies and the eggs hatch in from 13 days to 6 weeks, depending on the 

 temperature. The eggs are very tenacious of life and under favour- 

 able conditions may remain dormant for several months— from late 

 autumn to early spring. In warm weather and even during an open 

 winter, the larvae, or seed ticks, can live for several months indepen- 

 dently of their hosts. When they find the cattle, they fasten themselves 

 to the soft skin inside the thighs and flanks, etc., and are capable of 

 inducing the fever at this stage, although so small as to be scarcely 

 visible to the naked eye. After being on the animal for about a week 

 the first moult occurs and the nymph stage is reached, the parasite 

 having added one pair of legs posteriorly ; during this stage the sexual 

 organs develop, and at the second moult they are complete. Male 

 and female at this stage are of the same size. Copulation takes place 

 about two weeks after the 6-legged seed tick reaches its host, or 

 shortly after the second moult, after which the female slowly enlarges 

 for 6-20 days in summer and then rapidly increases in size in the 

 course of a day or two before dropping from the animal. In autumn 

 and winter, development occurs more slowly, the tick not falling off 

 for six weeks or more. After reaching the ground the female soon 

 begins to deposit eggs, thus completing the life-cycle, which requires 

 from 6-10 weeks in warm weather, and a much longer period during 

 the cold season. The females transmit the infection through their 

 eggs to their progency and the latter are capable of infecting any 

 susceptible animal to which they attach themselves ; the disease 

 therefore is not conveyed by the same ticks which take up the infected 

 blood, but only by their offspring. 



A descriptive list of 8 species of ticks found in the United States 

 is given, of which the first six are by far the most common, while only 

 the first-mentioned carries the fever in question. Boophilus {Mar- 

 garopus) annulatus (Texas-fever or cattle tick), readily distinguished 

 from the other seven ticks by the small size and reddish brown colour 

 of the head and shield ; found principally on cattle, less frequently 

 on horses, mules and asses, and in one case found on a deer. Ixodes 

 ricinus (castor-bean tick) has been collected from man, sheep, cattle, 

 goats, horses, deer, dogs, cats, foxes, rabbits, birds, and a few other 

 animals ; it was one of the first ticks studied and has a wide distribution 

 in the United States. Dermacentor reficulatus (net tick), found on 

 man, cattle, horses, sheep and deer, is most common in the w^est, 

 especially in California, Texas, and New Mexico. Dermacentor electus 

 (American dog tick or wood tick), found on man, cattle, dogs, horses, 

 rabbits and panthers, and has been collected in woods and on un- 



