Checking a company's vital signs before investing in its stock for dividend income is essential. If the underlying company isn't financially healthy, its dividend probably won't last very long.That won't be a problem with Johnson & Johnson (JNJ 0.39%) and Medtronic (MDT -0.53%). They're healthy companies that should continue to pay durable dividends in the decades ahead, making them great income investments. As healthy as it getsJohnson & Johnson is among the world's healthiest companies. The healthcare gia ...