There are many things that are simple and clear to doctors that are difficult for patients to understand, and because they lack the most basic medical knowledge or even a complete lack of common sense science, doctors have a hard time explaining them to their patients. So I came up with some easy-to-understand metaphors to explain medical issues that should be understandable to anyone who has common sense in life. I found them quite interesting, so I wrote them for the enjoyment of those who are interested in understanding them. 1. The cause and pathology of tuberculosis: Tuberculosis is a disease caused by the growth of tubercle bacilli (a bacterium) in the lung tissue and the destruction of lung tissue. It is like a wood with moths growing inside it. The moths will decay the wood and eat the wood inside, leaving many holes and pooping and peeing. When we use anti-tuberculosis drugs to treat tuberculosis, it is like using insecticides to kill the moths. If you wait until the whole wood is completely moth-eaten and full of holes before killing the moths, the wood will be completely rotten. The human lung is not wood, the lung has a certain ability to repair, but you should not think of it as too strong, its repair ability is not strong, a little more serious injury will be greatly wounded, unable to recover. Most patients with tuberculosis have lung lesions that cannot be completely eliminated. 2. Does the absence of TB bacilli in the sputum mean that it is not TB? Many patients are baffled by the fact that no TB bacilli are found in my sputum, but why do doctors insist that I have TB? In fact, this question is not a problem for doctors, and the answer is on the table. For example: a pond with some fish, I used the net to play a net, if the net came to one or several fish, I can certainly conclude that there are fish in the pond; then if I did not net fish, I can conclude that “there is no fish in the pond”? Everyone on earth knows: no. By the same token, if TB bacilli are found in the sputum of a patient, we can conclude that it is TB, but if TB bacilli are not found in the sputum, it does not mean that the patient does not have TB.