The little Frenchman Martin, the master builder, was another character in his way; a lively, energetic little fellow, whose eyes were everywhere. Not the driving in of a single nail escaped him. Yet, with all his watchfulness, he did more work than any three of his men. The habitual use of salt pork and beans, added to the total absence of vegetable diet during the long winter and summer, had caused scurvy to break out among the men, and poor Martin was suffering very much from it.According to the passage, what caused Martin’s illness?