工业硫酸锌的用途:为什么望梅能止渴???

吃梅止渴是非条件反射，望梅止渴和谈梅止渴是条件反射。

反射一般可以分为两大类：非条件反射和条件反射。根据信号系统的性质来划分，条件反射又可分为第一信号系统的反射和第二信号系统的反射。

非条件反射是指人生来就有的先天性反射。是一种比较低级的神经活动，由大脑皮层以下的神经中枢（如脑干、脊髓）参与即可完成。膝跳反射、眨眼反射、缩手反射、婴儿的吮吸、排尿反射等都非条件反射。梅子是一种很酸的果实，一吃起来就让人口水直流。这种反射活动是人与生俱来、不学而能的，因此属于非条件反射。

条件反射是人出生以后在生活过程中逐渐形成的后天性反射，是在非条件反射的基础上，经过一定的过程，在大脑皮层参与下完成的，是一种高级的神经活动，是高级神经活动的基本方式。多次吃过梅子的人，当他看到梅子的时候，也会流口水。这就是他在曾经吃过梅子流口水的基础上都能完成的，因此是条件反射。可以想像一下，如果当年曹操的士兵都没有吃过梅子，也从没有人告诉他们梅子是酸的，那将是什么样的一种结局。

根据引起条件反射的信号的类型，条件反射又可分为第一信号系统的反射和第二信号系统的反射。由各种视觉的、听觉的、触觉的、嗅觉的、味觉的具体信号引起的，叫做第一信号系统的反射。是人和动物共有的。

人类在与大自然斗争的过程中，在群体中产生了语言，大脑越来越发达，在大脑皮层形成了语言中枢，于是人类能对抽象的语言文字形成条件反射，这是是人类所特有的，属于第二信号系统的反射，例如谈梅止渴。

建立条件反射的过程如下：用无关刺激（如铃声）单独作用几秒钟，再用一非条件刺激（如进食）跟它结合，两者共同作用一定时间。结合若干次以后，单独使用无关刺激，就能引起原来由非条件刺激引起的反应（如分泌唾液），这里铃声已经变成分泌唾液的条件刺激，条件反射就形成了。

非条件反射是条件反射的基础，条件反射提高了动物对环境的适应能力，大脑越发达的动物，建立的条件反射也就越复杂。

望梅止渴

有一年夏天，曹操率领部队去讨伐张绣，天气热得出奇，骄阳似火，天上一丝云彩也没有，部队在弯弯曲曲的山道上行走，两边密密的树木和被阳光晒得滚烫的山石，让人透不过气来。到了中午时分，士兵的衣服都湿透了，行军的速度也慢下来，有几个体弱的士兵竟晕倒在路边。

曹操看行军的速度越来越慢，担心贻误战机，心里很是着急。可是，眼下几万人马连水都喝不上，又怎么能加快速度呢？

他立刻叫来向导，悄悄问他：“这附近可有水源？”向导摇摇头说：“泉水在山谷的那一边，要绕道过去还有很远的路程。”曹操想了一下说，“不行，时间来不及。”他看了看前边的树林，沉思了一会儿，对向导说：“你什么也别说，我来想办法。”他知道此刻即使下命令要求部队加快速度也无济于事。脑筋一转，办法来了，他一夹马肚子，快速赶到队伍前面，用马鞭指着前方说：“士兵们，我知道前面有一大片梅林，那里的梅子又大又好吃，我们快点赶路，绕过这个山丘就到梅林了！”士兵们一听，仿佛已经吃到嘴里，精神大振，步伐不由得加快了许多。

故事出自《世说新语·假谲》。成语“望梅止渴”，比喻用空想安慰自己或他人。

Quenching Thirst by Watching Plums Cao Cao of the Three Kingdoms period (220-265) was　not only a capable politician in managing state affairs, but also a strategist good at　leading troops in going to war. 　

One summer, Cao Cao was leading his troops in a punitive expedition against Zhang Xiu.

It was extraordinarily hot. The burning sun was like a fire, and the sky was cloudless. The　soldiers were walking on the winding mountain paths. The dense forest and the hot rocks　xposed to the sun on both sides of the paths made the soldiers feel suffocated. By noontime　the soldiers' clothes were wet through with sweat, and the marching speed slowed down. Some　solders of weak physique even fainted on the roadside. 　　

Seeing that the marching speed was slower and slower, Cao Cao was very worried because he　feared that he might bungle the chance of winning the battle. But how could they quicken　their speed? Cao Cao at once callde the guide and asked him on the quiet whether there was a　source of water nearby. The guide shook his head, saying that the spring water was on the　other side of the mountain, which was very far to have to make a detour to reach. Cao Cao　realized that time didn't permit them to make such a detour. After thinking for a moment, he　said to the guide, "Keep quiet. I'll find a way out." He knew that it would be to no avail to order his troops to quicken the steps. He had a brain wave and found a good solution. He　spurred his horse and came to the head of the column. Pointing his horsewhip to the front, Cao Cao said, "Soldiers, I know there is a big forest of plums ahead. The plums there are both big and delicious. let's hurry along, and we will reach the forest of plums after bypassing this hill." When the solders heard this, they immediately slobbered. Picturing in their minds the sweet and sour flavour of the plums, the soldiers felt as if they were actually eating the plums, the soldiers felt as if they were actually eating the plums themselves. The morale greatly boosted, the soldiers quickened their steps a great deal automatically. 　　This story comes from "The Fake Tangery" in Anecdotes of This World by Liu Yiqing of the Southern Dynasties period (420-589). From this story, people have derived the set phrase "quenching thirst by watching plums" to refer to trying to comfort oneself of others by idle dreams.

条件反射，看到梅子流口水

条件反射

建立了以视觉为基础的条件反射