The evidence offered in the first of these studies indicative of a causative relationship between Rickettsia ruminantium and heartwater is supplemented by the following observations concerning the ticks which carry the disease.

When larvæ, which had taken no food since hatching, were allowed to feed upon cases of heartwater, they acquired Rickettsiœ which appeared to be identical with those in the tissues of animals suffering from heartwater, whereas control larvæ hatched from eggs deposited by the same female and fed on normal animals remained free of Rickettsiœ.

After larvæ presumably infective had moulted, the resultant nymphæ containing Rickettsiœ in their alimentary tracts, when fed upon susceptible animals produced in them typical attacks of heartwater, which the control nymphae, devoid of Rickettsiœ, failed to do. The tissues of animals thus infected were found upon histological examination to contain typical Rickettsioelig;.

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