[简答题]简述密性试验的目的以及方法。

女，39岁。主诉突发剧烈头痛半个月，伴意识障碍，右侧肢体活动减少1周。入院半个月前患者与家人聊天时突感剧烈头痛，呈持续胀痛，不能忍受，急到私人诊所，测血压为200／100mmHg。半小时后出现意识丧失，肢体强直抽搐，口吐白沫，持续约10分钟自行缓解。急送当地医院行头颅CT检查示颅内出血，腰穿检查示血性脑脊液（具体不详），给予药物治疗，头痛缓解。1周后患者出现昏睡，表情淡漠，不能言语，同时出现右侧肢体活动减少。入院查体：呈昏睡状态，颈强直。克氏征、布氏征阳性。右侧肢体肌力Ⅱ级，右侧巴氏征（+）。

W: I enjoy going through second-hand bookstores, don’t you It’s interesting to see what people used to enjoy reading. Did you see this old book of children’s stories
M: Some of these books are not so old, see This mystery was published only six years ago. It costs 75 cents. You can’t beat that.
W: Here, look at this.
M: What Are you getting interested in the 19th century poetry all of a sudden
W: Everything on that shelf is worth 50 cents. But if this is the signature of someone who was well-known, it might bring a lot more. I hear William Shakespeare’s signature is worth about a million dollars.
M: Oh, I can hardly read what that one says. Who wrote it
W: The name looks like Harold Dodgson, maybe. Wasn’t he a politician or something I am going to buy this book and see if I can find a name like that in the library.
M: Good luck. Your poetry may make you rich, but I’ll bet my 75-cent