INFECTIOUS DISEASES OF CATTLE. 467 



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 attaek. The 

 disease exerts but little effect on the stomach and intestines beyond 

 more or less reddening of the mucous membrane; hence an exami- 

 nation 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 noninf ected 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. XLVIII, XLIX, and L.) — The cattle tick is, as its name indi- 

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

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

 (BoophUus), 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 (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 

 within the shell it ruptures this and gains its freedom. The time 

 required from the laying of the eggs to their hatching varies consid- 

 erably, according to the temperature. In the laboratory in the heat 

 of midsummer this was accomplished in. about thirteen days. In the 

 late fall, under the same conditions, it required from four to six weeks. 

 The larva after emerging from the egg is very minute, six -legged, and 

 just visible to the naked eye. (PI. XLVIII, fig. 3.) If these larvae 

 be kept on a layer of moist sand or earth in a covered dish, they may 

 remain alive for months, but there is no appreciable increase in size. 

 As soon, however, as they are placed upon cattle growth begins. 



On pastures these little creatures soon find their way onto cattle. 

 They attach themselves by preference to the tender skin on the 

 escutcheon, the inside of the thighs, and on the base of the udder. 

 Yet when they are very numerous they may be found in small num- 

 bers on various parts of the body, such as the neck, the chest, and 

 the ears. (PI. XLIX.) 



The changes which they undergo during their parasitic existence 



