486 DISEASES OF CATTLE. 



now has on the surface a paler yellowish hue. ^Vlien it is incised 

 this yellowish tinge, or mahogany color, as it has been called by 

 some, is still more prominent. This is due to the large amount of 

 bile in the finest bile capillaries, and as these are not uniformly filled 

 with it the cut surface has a more or less mottled appearance. This 

 bile injection causes in many cases a fatty degeneration of the liver 

 cells, which makes the organ appear still lighter in color. 



In all cases the gall bladder should be examined. This is dis- 

 tended with bile, which holds in suspension a large quantity of 

 yellow flakes, so that when it is poured into a tall bottle to settle fully 

 one-half or more of the column of fluid will be occupied by a layer 

 of flakes. If mucus is present at the same time, the bile may become 

 so viscid that when it is poured from one glass to another it forms 

 long bands. The bile in health is a limpid fluid containing no solid 

 particles. 



If the animal has not been obsei'ved during life to pass urine 

 colored with blood or red water, the bladder should be opened. This 

 quite invariably, in acute cases, contains urine which varies in color 

 from a deep port wine to a light claret. In many cases the color is 

 so dense that light will not pass through even a thin layer. (PI. 

 XLVII, fig. 3.) The kidneys are always found congested in the 

 acute attack. The disease exerts but little effect on the stomach and 

 intestines beyond more or less reddening of the mucous membrane; 

 hence an examination of these may be safely omitted. The lungs 

 are, as a rule, not diseased. The heart usually shows patches of 

 blood extravasation on the inside (left ventricle) and less markedly 

 on the outer surface. 



We have observed jaundice of the various tissues but very rarely. 

 It has been observed by some quite regularly, however. 



During the hot season about 90 per cent of the susceptible mature 

 animals from a noninfected district die, but later, in the cool weather, 

 the disease assumes a milder type, with a consequent decrease in the 

 number of deaths. 



The cattle tick, Margaropns annulatus, as the carrier of Texas fever. 

 (Pis. XLVIII, XLIX, and L.) — The cattle tick is, as its name indi- 

 cates, a parasite of cattle in Ihe southern part of the United States. 

 It belongs to the group of Arthropoda and to the genus Margaropns 

 (or Boophilus), which is included in the order Acarina. Its life 

 history is quite simple and easily traced from one generation to an- 

 other. It is essentially a parasite, attaching itself to the skin (PI. 

 XLIX) and drawing the blood of its host. It is unable to come to 

 maturity and reproduce its kind unless it becomes attached to the 

 skin of cattle, whence it may obtain its food. 



The eggs laid on the ground after the female has dropped from the 

 host begin to develop at once. When the embryo is fully formed 



