He hesitated an instant, then responded quietly, "Nurses have to know the truth, of course, and I am sure that you have a brave little heart, so I'm not afraid to tell you that it _is_ bad. It is almost sure to be fatal, in time, but not necessarily soon. If he will take things easy, as I told him to, he'll live for a considerable time yet; but we mustn't allow him to get very greatly excited, or do any very heavy work." Suddenly very white, but calm and tearless, Smiles answered, "I reckon I can help him better if I know all about it, doctor. I _got_ to help him, you know. He's all I have now in the whole world." "Of course you're going to help him--we both are--but ... you have me, little sister, and your life work," he answered with awkward tenderness. "Now let us see if I can make you understand what I believe the trouble to be. In its incipient--that is, its early stages, it would be rather hard to tell from angina pectoris, for the symptoms would be much the same--pain about the heart and shortness of breath. But one can get over the latter, and feel perfectly well between attacks." He picked up from his open suitcase a folded newspaper which he had tossed in half read, on leaving the city, and drew for her a crude diagram of the heart and major arteries. "This biggest pipe which goes downward from the heart is called the great artery, and it and its branches--just like a tree's--carry the blood into all parts of the body, except the lungs. Another name for it is the descending thoracic aorta, and that is where grandfather's trouble is. If you knew something about automobile tires I would explain it by saying that he had a blow-out, but it's something like this. The pipe has an outer surface and an inner lining. At one time or another something happened to injure and weaken the former--disease does it sometimes--perhaps it may have been a severe strain or crushing blow on his chest." "A big tree fell on him early last winter," cried Rose, with sudden enlightenment. "His chest is so big and strong that he didn't think that it hurt him, 'cept to lame him considerable." "That may have caused the trouble. Well, what happens is this. The blood is pumped by the heart through that weakened pipe, and, little by little, it forces the lining out through the weakened spot, making something like a bubble filled with blood. In time that might grow until you could actually see the swelling, and all the time, the containing tissue is getting thinner and thinner. Now you can yourself guess the reason why he mustn't do anything to over-exert his heart. Hard work, or great excitement, makes our hearts beat faster, and sends the blood through that big artery with extra force and ..." "The bubble might ... break," whispered "Smiles," with a frightened look on her young face. "Yes. We call it a rupture of the aneurism, and when that happens mortal life ends."