You have to look at this in context:
The Cinghalese, as I have said before, are a very sensitive people. Any grievance rankles in their bosom, and in revenge they will not unfrequently use the knife. An Eurasian friend, a doctor, says that he quite thinks cases might occur in which a man who had been wounded or assaulted by another would die out of spite in order to get the other hanged! — would connive with his relations and starve himself, and not try to heal the wound. He says however that the cases of ruptured spleen — of which we so frequently hear — are genuine, as frequent fevers often cause immense enlargement of the spleen, which then bursts for a comparatively slight cause, e.g. a planter and a stick.
The doctor has been speaking of cases in which parties wounded by assault with a knife deliberately starve themselves and leave the wound untreated in order to increase the severity of the injury—they are even willing to die of the wound if it gets the assailant hanged. But he qualifies this by pointing specifically to cases of ruptured spleen: in these even a minor injury, such as a beating by a planter with a stick? rather an assault with a knife, may genuinely have a deadly effect, because prior fever has made the victim unusually vulnerable.
? I take the (English) planter to be the agent delivering the beating, because it is the possibly self-induced death of Cinghalese which is at issue. However, the planter may rather be the victim, if the doctor means that Europeans are particularly susceptible to fevers and consequent splenomegaly.