On Thursday morning, Zhaxi appeared at the door of Yang Ping’s office.
He clutched a notebook filled with twenty pages of findings he gathered from last night’s research. He barely slept all night, not because he didn’t want to, but because fragnts in his mind spun too intensely, seeing Professor Zhou slumped over the desk whenever he closed his eyes, noticing the ashen fingertips.
Yang Ping arrived at seven, saw Zhaxi standing at the door, hesitated for a mont, then looked at his watch: "What ti did you get here?"
"I ca to the departnt at six."
"What ti did you go to sleep last night?"
Zhaxi hesitated for a mont, didn’t dare to lie: "After eleven."
Yang Ping nodded, opened the office door, walked in, sat in his chair, and pointed to the seat opposite him: "Go ahead."
Zhaxi sat down, opened the notebook, took a deep breath, and began to speak. He sorted out all the information he found last night according to his understanding: the typical clinical manifestations of organic phosphorus poisoning, cholinergic symptoms, nicotinic symptoms, central nervous system symptoms; constriction of the pupils is the most characteristic manifestation of cholinergic symptoms, caused by parasympathetic nervous excitation; characteristics of skin contact absorption, long latency, atypical symptoms, local manifestations preceding systemic manifestations; organic phosphorus-induced skin darkening disease, prolonged exposure can result in ashen pigntation at the fingertips and face.
When he finished, he looked up at Yang Ping.
Yang Ping listened, was silent for a long ti, then took a blank sheet of paper from a drawer, placed it on the desk, and picked up a pen.
"What you said is all correct, but you missed a crucial issue." He wrote a word on the paper: dosage.
"Organic phosphorus poisoning, whether acute or chronic, hinges on dosage. How high a concentration is needed for skin contact absorption to reach a lethal dose? How long must the contact ti be? How large an area of the skin?" He looked at Zhaxi, "Did you check these numbers?"
Zhaxi was stunned; he hadn’t checked.
Yang Ping was interested in the case and saw it as an opportunity to cultivate Zhaxi’s reasoning skills, as an excellent doctor must possess strong reasoning abilities.
Yang Ping didn’t criticize him but drew a table on the paper: "The toxicity of organic phosphorus compounds is asured by LD50, the dian lethal dose. The toxicity varies by hundreds of tis among different varieties of organic phosphorus. For example, malathion has an LD50 of about 1000mg/kg, which is considered low toxicity; whereas parathion, with an LD50 of only 3mg/kg, is highly toxic. Why did Dr. Yuan co to consult us? Because their analysis has confird that it was impossible for the deceased to have ingested a large amount of organic phosphorus, so they are puzzled and ca to us for advice."
He filled in a few numbers in the table, then looked up: "So, you need to clarify one question: if the cause of death was skin contact absorption, which type of organic phosphorus is required? What concentration? How long was the contact?"
Zhaxi opened his mouth, but couldn’t answer.
Yang Ping put down the pen, leaned back in his chair: "And there’s another question. You said the deceased had pigntation at the fingertips consistent with long-term organic phosphorus exposure. But long-term exposure usually results in chronic poisoning symptoms, such as fatigue, loss of appetite, weight loss, mory decline, and mood changes. Did you find corresponding evidence of these manifestations in the deceased?"
Zhaxi thought for a mont: "His students said he has lost weight over the last six months and was becoming more and more silent."
Yang Ping nodded: "Yes, but these are non-specific manifestations. Many illnesses can lead to weight loss and personality changes. What you need to find is more specific evidence." He paused and asked a question Zhaxi hadn’t anticipated: "Did the deceased have a physical examination? Where is the health report from the last six months? This is another reason why Dr. Yuan consulted us. As a forensic doctor, Dr. Yuan’s knowledge of toxicology surely surpasses that of doctors, but they lack knowledge about diseases caused by toxins, or conditions pre-existing in conjunction with toxin exposure."
Zhaxi was montarily stunned: "That... I don’t know."
Yang Ping picked up the phone on the desk and dialed a number: "Dr. Yuan, this is Yang Ping. There are two things I need your help with. First, can you retrieve the deceased’s health reports from the last six months? Yes, all of them. Second, were any bottles of organic phosphorus compounds, dications, or laboratory records found at the deceased’s ho or laboratory? Okay, I’ll wait to hear back from you."
After hanging up, he looked at Zhaxi: "Investigating a case is like diagnosing an illness; you can’t rely solely on guessing. You need evidence. Every clue must have corresponding evidence to support it. A hypothesis without evidence is rely speculation; although speculation can serve as a hypothesis, it requires validation."
Zhaxi lowered his head and wrote a line in his notebook: Evidence chain, each must be supported by evidence.
At nine in the morning, Dr. Yuan called back, and Yang Ping turned on the speakerphone so Zhaxi could also listen.
"Professor Yang, we’ve retrieved the health reports. We have the deceased’s reports from the last three years, and the examination dates were consistent each year. The most recent was four months ago, and the report shows: weight fell six kilograms from the previous year, blood pressure slightly low, blood cholinesterase..."
Yang Ping suddenly sat up straight: "What was the blood cholinesterase level?"
Dr. Yuan flipped through the report: "The normal range is 4000-12000U/L, and his result was 2100. The report noted it was low, but the doctor didn’t take special action, just recomnded a follow-up."
Yang Ping continued to inquire: "What about the previous two years?"
"Two years ago, it was normal at 6800, but it started decreasing last year to 3800."
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