And even in the intervals of health the asthmatic's sufferings do not cease: he seems well, he goes about like his fellows and among them, but he knows that he is altogether different from them; he bears about his disease within him wherever he goes; he knows he is struck -- "haeret lateri lethalis arundo;" he is conscious that he is not sound -- he cannot be warranted; he is not certain of a day's, perhaps not of an hour's health; he only knows that a certain percentage of his future life must be dedicated to suffering; he cannot make an engagement except with a proviso, and from many of the occupations of life he is cut off; the recreations, the enjoyments, the indulgences of others are not for him; his usefulness is crippled, his life is marred; and if he knows anything of the nature of his complaint, he knows that his sufferings may terminate in a closing scene worse only than the present." Henry Hyde Salter.Source: Salter, Henry Hyde, "On Asthma: It's Pathology and Treatment," 1882, New York, page 2
Note: "haeret lateri lethalis arundo," is Latin. Translated into English it means "in her side still clings that deadly shaft." Or, worded another way by eudict.com: "The deadly arrow sticks in her (his) side." Asthma is like the deadly arrow that clings to her side wherever she goes. Asthma clings to you no matter where you go, no matter what you do. It's always there hovering over you like a dark, ominous cloud.
According to http://www.proz.com, it comes from Virgil's Aenid (book 4, string 73):
Sick with desire, and seeking him she loves, From street to street the raving Dido roves. So when the watchful shepherd, from the blind, * Wounds with a random shaft the careless hind, * Distracted with her pain she flies the woods, Bounds o'er the lawn, and seeks the silent floods, With fruitless care; for still * the fatal dart Sticks in her side *, and rankles in her heart.