Quite a while ago, we had a thread about scurvy.
In 1739 Lord Anson circumnavigated the globe. A thousand sailors died of scurvy. Wow posted having read that officers didn't get scurvy because they could
afford orange marmelade, which was too expensive to give the crew. The officers believed that poor hygiene was cause of death of the sailors. In 1754 Lind published his Treatise on scurvy.
But only after forty more years did the Admiralty compel
giving sailors lemon juice.
If Dana was making a joke about scurvy being caused by poor hygiene, it was a very bad joke. He doesn't mention what kept him from getting scurvy. I don't remember any metion of fruit except "plum duff". And I don't remember any mention of vegetables. They did get fruit at Juan Fernandes. Elsewhere I have read that it could take six months on a deficient diet for symptoms to appear.