41 



feeding or resting at but little distance from the roots of the wool. A 

 dozen or more of these ticks, which were moderately well fed when 

 taken from the sheep were, with some wool, placed in a cotton-stoppered 

 bottle and kept in a room with a temperature varying between 60° and 

 80° Fab. They all died in less than four days. The leanest succumbed 

 first, in abont two days, while those that were better nourished grad- 

 ually grew smaller and thinner, and lived little longer than the third 

 day. Others placed in wool over the damp soil of a geranium in a 

 flower-pot died within four days. On the other hand, some young ones 

 which were hatched out in a bottle were kept for nearly two weeks, or 

 until their daily feeding was neglected. To feed them they were placed 

 on the back of my hand. By this means I could, with a lens, watch 

 them bore into the skin and see the abdomen slowly enlarge as they 

 drew in the blood. They had some difficulty in penetrating the thick 

 skin, but usually succeeded by slipping their tube into a hair follicle. 

 At first no itching or irritation was felt, except a slight twinge when 

 the bills first penetrated the skin ; but little swellings came on a day or 

 two later which itched for over a week. The itching was far more per- 

 sistent than with mosquito bites. They must in this way cause lambs 

 much discomfort. It was at first thought that a fluid could be seen 

 running from the parasite to the hand through the bill, but no more was 

 thought of it until the elevations began to rise and itch ; then it ap- 

 peared certain that the little pests had secreted a poisonous fluid. The 

 office of this secreted fluid is probably to assist the flow of blood by 

 keeping it from clotting. 



The above experiments show that the parasite spends its whole life 

 on the sheep. 



Source of contagion. — The fact that this parasite passes its whole life op 

 the sheep, and that it produces but few young, are very important con- 

 siderations in efforts for exterminating the pest and preventing a new 

 infection. They indicate that if all are killed the sheep will not again 

 be infected except from other sheep. 



Z>*se«se.^The injury sustained by sheep from these parasites varies 

 according to the number present. It arises from the itching and pain 

 inflicted by them when obtaining their food. A few cause but little 

 annoyance, and, were it not that these may become the source of future 

 multitudes, would be scarcely worth noticing. To lambs the annoy- 

 ance is particularly aggravating, as their skin is tender and the number 

 of parasites attacking them after shearing is unusually large. In older 

 sheep the irritation is the more noticeable towards spring. At this time 

 the parasites are more numerous and the animals bite and scratch them- 

 selves oftener. 



Medical treatment.— The well-known means of ridding the sheep of 

 these pests are the tobacco or other mixtures used for scab-dips. The 

 best time of the year to dip is at shearing time. Then the older sheep 

 can easily be handled and cleansed. The dipping should not be delayed 



