EPIDEMIOLOGY 589 



sheds its skin and becomes sexually mature. It is at this age that 

 males and females are with certainty distinguishable for the first 

 time. The males emerge from the skin as brown, oval ticks, about 

 one-tenth of an inch in length. He has reached the limit of growth 

 and goes through no further development. Later he shows great 

 activity in moving about over the skin of the host. The female at 

 the time of molting is slightly larger than the male. She seldom 

 shows much activity, seldom moving far from her original point of 

 attachment. She still has to undergo most of her growth. After 

 mating the female increases very rapidly in size, and in from twenty- 

 one to twenty-six days after attaching to a host as a seed tick she 

 becomes fully engorged and drops to the ground of the pasture, to 

 repeat the cycle of development. 



"To sum up, on the pasture there are found three stages of the 

 tick the engorged female, the egg, and the larva; and on the host 

 (cattle) are found four stages the larva, the nymph, the sexually 

 mature adult of both sexes, and the engorged condition of the female. 



"In undertaking measures for eradicating the tick it is evident 

 that the pest may be attacked in two locations, namely, on the pasture 

 and on the cattle. 



"In freeing pastures the method followed may be either a direct 

 or an indirect one. The former consists in excluding all cattle, 

 horses, and mules from pastures until all the ticks have died of star- 

 vation. The latter consists in permitting the cattle and other animals 

 to continue on the infested pasture and treating them at regular 

 intervals with oils or other agents destructive to ticks and thus pre- 

 venting engorged females from dropping and reinfesting the pasture. 

 The larvae on the pasture, or those which hatch from eggs laid by 

 females already there, will all eventually meet death. Such of these 

 as get upon the cattle from time to time will be destroyed by the 

 treatment, while those which fail to find a host will die in the pasture 

 from starvation. 



"Animals may be freed of ticks in two ways. They may be treated 

 by solutions, etc,, that will destroy all the ticks present, or they may 

 be rotated at proper intervals on tick-free fields until all the ticks 

 have dropped." 



Epidemiology. A number of points in the epidemiology of Texas 

 fever, formerly quite mysterious and unexplainable, are now easily 

 understood, since the etiology of the disease has been cleared up. 

 Wherever Texas fever or piroplasmosis of cattle has occurred it 

 was observed that animals on the pastures are more commonly 

 attacked than animals kept in barns. It was also noticed long ago 

 that a wet, marshy ground upon which cattle entered in spring 

 formed a favorable soil for the appearance of the disease. Hot 

 weather favors outbreaks more than a cool temperature. Animals 

 born and raised in infected territories are much more resistant than 

 animals born and raised in a free territory and later brought to the 



