478 DISEASES OF CATTLE. 



in the healthy state, has lost its natural brownish color (fig. 1), and 

 now has on the surface a paler, yellowish hue. When it is incised' 

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

 some, is still more prominent. This is owing to the large quantity 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 number 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 during life has not been observed 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 e^en a thin layer. (PI. 

 XLV, 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 them 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, Margaropus annulatus, as the carrier of Texas 

 fever. (Pis. XLVI, XL^^I, and XL VIII.)— The cattle tick is, as 

 its name indicates, a parasite of cattle in the southern ixirt of the 

 United States. It belongs to the group of Arthropoda and to the 

 genus Margaropus (or Boophilus), which is included in the order 

 Acarina. Its life history is quite simple and easily traced from one 

 generation to another. It is essentially a parasite, attaching itself to 

 the skin (PL XL VIII) 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. 



