486 DISEASES OF CATTLE. 



from getting on the cattle until sixty days after their inoculation or 

 until they have fully recovered, at which time a few ticks may be 

 placed upon them in order to reenforce their immunity. Naturally 

 this time varies according to the type of the attack. As the best 

 results with these immunizing experiments have been obtained in 

 cool weather and with young cattle, it is recommended that animals 

 from 6 to 15 months old be selected for inoculation, and that they be 

 immunized during the late fall or winter months, in order that they 

 may enter tick-infested pastures in the spring without danger. 



TEXAS FEVER. 



[Description of plates.] 



Plate XL VI. Fig. 1. Spleen of an acute fatal case of Texas fever. The narrow 

 end of the spleen is here represented. Fig. 2. Spleen of healthy steer. Though 

 the latter animal weighed one-half more than the former, the weight of the diseased 

 spleen (61 pounds) was nearly three times that of the healthy spleen (2f pounds). 



Plate XL VII. Fig. 1. The cut surface of a healthy liver taken from a steer 

 slaughtered for beef. Fig. 2. The cut surface of the liver in Texas fever. Fig. 3. 

 Appearance of the urine in an acute fatal case of Texas fever. Fig. 4. Red cor- 

 puscles, magnified a thousand diameters, containing the parasite of Texas fever. 

 This appears as a blue point a near the edge of the corpuscle. The blood was 

 taken from a skin incision. The case was nonfatal and occurred late in fall. 

 Fig. 5 . Red corpuscles from the blood of an acute fatal case, twenty hours before 

 death. The Texas fever microbes a are shown as pear-shaped bodies, stained with 

 methylene blue, within the red corpuscles. The larger body on the right & is a 

 white blood corpuscle, also stained with methylene blue. Magnified a thousand 

 diameters. 



Plate XL VIII. The cattle tick, the carrier of Texas fever. Fig. 1. A series of 

 ticks, natural size, from the smallest, just hatched from the egg, to the mature 

 female, ready to drop off and lay eggs. Fig. 2. Eggs, magnified 5 times. Fig. 3. 

 The young tick just hatched, magnified 40 times. Fig. 4. The male after the last 

 molt, magnified 10 times. Fig. 5. The female after the last molt, magnified 10 

 times. Fig. 6. A portion of the skin of the udder, showing the small ticks. From 

 a fatal case of Texas fever produced by placing young ticks on the animal. Nat- 

 ural size. Fig. 7. A portion of the ear of the same animal, showing same full- 

 grown ticks ready to drop off. Natural size. 



Plate XLIX. Portion of a steer's hide, showing the Texas fever tick (Mar- 

 garopus annulatus) of the United States. Natural size. Original. 



Plate L. Fig. 1. Dorsal view of male Margaropus annulatus of the United 

 States, greatly enlarged. Original. Fig. 2. Ventral view of male Margaropus 

 annulatus of the United States, greatly enlarged. Original. Fig. 3. Dorsal 

 view of replete female Margaropus annulatus, greatly enlarged. Original. Fig. 4. 

 Ventral view of same. 



Plate LI. Map of the United States, showing the region infected with Texas 

 fever. The shaded and black portions show the area quarantined on account of 

 this disease. Cattle may not be shipped interstate from the shaded area between 

 January 31 and November 1 except for immediate slaughter. In the black areas 

 the infection is slight, as a result of the work being done for the extermination of 

 the cattle ticks, and cattle officially inspected and found free from infection may 

 be shipped interstate therefrom for any purpose. As the quarantined area is sub- 

 ject to change at any time, this map should be compared with the latest regula- 

 tions, which may be obtained at any time on application to the Secretary of 

 Agriculture. 



