Redwater in Cattle. 
145 
passed into the body of the healthy cattle on which they pass 
the next stage of their development. 
In the light of these discoveries, many points in connection 
with the pathology of redwater that were once obscure can 
now be quite satisfactorily explained. The disease is rare or 
unknown on cultivated land because ploughing and cropping 
interfere with the multiplication of ticks. It is a disease of 
moor-land and rough permanent pasture because these are places 
in which ticks can maintain their existence from year to year, 
provided that they can find cattle to which they may attach 
themselves. The disease is specially one which attacks cattle at 
grass, because housing secludes cattle from the attacks of ticks. 
It is a disease of summer and autumn because these are the 
seasons during which ticks are active. 
One or two other points have still to be considered. On 
some redwater farms the only losses occasioned by the disease 
are among bought-in cattle, those bred on the farm appearing 
to escape infection. In such cases the majority or the whole 
of the cattle reared on the farm have not escaped the disease, 
but have become infected as calves or yearlings, at which age 
cattle are but little susceptible, and generally do not develop 
any symptoms of illness when bitten by infected ticks. 
An animal which has passed through an attack of redwater 
is protected for a long time afterwards, and possibly for life, 
against a second attack. Nevertheless, such an animal 
continues to have small numbers of the redwater parasites in 
its blood, as may readily be proved by injecting some of this 
into a healthy animal. This is true even of those cases in 
which infection has taken place during calf-life, and in which 
the animal has never been observed to be ill. Hence it 
follows that cattle removed from a redwater farm to another 
may carry the disease to the latter, provided it is one on which 
ticks exist ; for these would become infected in sucking the 
blood of the imported animals, and their immediate progeny 
would be capable of infecting the cattle reared on the 
farm. 
Although the investigations of recent years have thrown 
clear light on the cause of redwater, the prevention of the 
disease is still in most cases a difficult problem. As in natural 
circumstances there is no redwater without ticks, it might be 
supposed that measures directed against them ought to have 
an important part in any plan of prevention. Unfortunately, 
however, there has not yet been discussed any practicable means 
of eradicating ticks except by keeping animals off the land 
for a period which exceeds the longest possible life-time of a 
tick. In all probability a complete year would suffice for this 
purpose, and it may be accepted as practically certain that two 
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