206 Annual Report for 1907 of Royal Veterinary College. 
assistance in ascertaining the cause of chronic diarrhoea among 
deer kept in a park, and when one of the diseased animals was 
killed the post-mortem examination unexpectedly disclosed the 
fact that it was the subject of Johne’s disease. 
The fact that deer may suffer from the disease is not one 
of much direct interest, but it is of importance as suggesting 
that other ruminants, such as the sheep, may not be immune. 
It is intended to carry out experiments to test this possibility. 
Redwatbr in Cattle. 
In a previous Annual Report (Vol. 66, page 143), an account 
was given of the pathology of this disease, including some 
hints regarding measures of prevention. The disease is again 
referred to here because it has been found that the old 
erroneous opinions regarding its cause are still widely held. 
It must therefore be repeated that redwater is caused by a 
microscopic blood parasite which is transferred from affected 
to healthy cattle by means of ticks. It is the fact that ticks 
play an essential role in the causation of the disease that 
explains the peculiar regional and seasonal occurrence of cases 
of redwater. 
Cattle of any age can be infected with redwater, but, 
whereas the disease is generally severe and frequently fatal in 
adults or animals over two years of age, it is of so mild a 
character in calves or animals under a year old that it generally 
fails to excite in them any visible disturbance of health. As 
one attack of the disease tends to render an animal insus- 
ceptible, cattle which are infected during early life rarely 
afterwards become visibly affected or die, even although they 
are grazed on notoriously dangerous ground. Nevertheless 
these animals are not entirely free from the disease, for the 
rule is that when once an animal has been infected it ever 
afterwards, or at any rate for years, continues to harbour the 
minute parasites which are the cause of redwater. This may 
in most cases be readily proved by using a small quantity of 
their blood for the inoculation of a healthy adult ox, the 
almost invariable result being that the inoculated animal 
develops the symptoms of redwater after about a week. On 
what may be called redwater pasture the animals which were 
infected while young tend to perpetuate the disease, for ticks 
in sucking their blood become infective and pass the parasites 
on to other animals on the same pasture. 
These facts give the clue to the prevention of the disease. 
If ticks could be eradicted from any given pasture, redwater 
would thereby be stamped out, but in actual circumstances 
such eradication is usually difficult. It may, however, be 
achieved by keeping cattle and other animals off the pasture for 
