CHAPTER XXIII 



External Parasites of Animals 



The many diseases of farm live-stock cannot be treated in a book 

 of this kind, and very brief advice might be more dangerous than useful ; 

 but the ticks, lice, fleas, and similar things that infest animals may be 

 included. The spraying of live-stock is as important, in many cases, as 

 the spraying of plants. 



Handling the cattle-tick, or Texas-fever tick (Margaropus annulatus) 

 (H. W. Graybill, Bur. Animal Ind., U. S. Dept. Agric.) 



On the pasture there are three stages of the tick — the engorged 

 female, the egg, and the larva ; and on the host are four stages — the 

 larva, the nymph, the sexually mature adult of both sexes, and the 

 engorged condition of the female. 



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

 with an agent 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. 



Dips for cattle-ticks, their preparation and use 



Crude petroleum. — Various kinds of crude petroleum have been 

 used with more or less success in destroying ticks. The heavier 

 varieties of oil are very injurious to cattle. On the other hand, the 

 very light oils are so volatile that their effect lasts but a short time 

 thus rendering them less efficient. The petroleum known as Beau- 

 mont oil, obtained from Texas wells, has given the best results. The 

 best grade of this oil to use is one that has a specific gravity ranging 

 from 22j° to 24^° Beaume, containing \\ to I2 per cent of sulfur, 

 and 40 per cent of the bulk of which boils between 200° and 300° C. 

 The oil may be applied by employing a spray pump or a dipping vat. 



Animals that have been dipped in crude oil, especially during warm 



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