According to Princeton historian J.E. Seigel, in his late teens, Marx may have had pneumonia or pleurisy, the effects of which led to his being exempted from Prussian military service. In later life whilst working on "Das Kapital" (which he never completed), Marx suffered from a trio of afflictions. A liver ailment, probably hereditary, was aggravated by overwork, a bad diet, and lack of sleep. Inflammation of the eyes was induced by too much work at night. A third affliction, eruption of carbuncles or boils, "was probably brought on by general physical debility to which the various features of Marx's style of life – alcohol, tobacco, poor diet, and failure to sleep – all contributed. Engels often exhorted Marx to alter this dangerous regime". In Professor Siegel's thesis, what lay behind this punishing sacrifice of his health may have been guilt about self-involvement and egoism, originally induced in Karl Marx by his father.