discovery

土豆一旦发了芽，即含有一种叫龙葵素的有毒物质，这种毒素会使人呕吐、 腹泻，甚至抽搐、昏迷。 　　因此，土豆发了芽就不应食用。

discovery

正常土豆中龙葵素的含量较少，为2－10毫克％。当土豆发芽后皮肉变绿，龙葵素含量增高。人一次食用0.2~0.4克可发生中毒。

中毒表现

　　一般在进食后十分钟至数小时出现症状，胃部灼痛，舌、咽麻，恶心，呕吐，腹痛，腹泻，严重中毒者体温升高，头痛，昏迷，出汗，心悸。儿童常引起抽风、昏迷。

预防措施

⑴土豆应贮存在低温、通风、无直射阳光的地方，防止生芽变绿。
⑵生芽过多或皮肉大部分变黑、变绿时不得食用。
⑶发芽很少的土豆，应彻底挖去芽和芽眼周围的肉。因龙葵素溶于水，可侵入水中泡半小时左右。

discovery

The potato is part of the nightshade family and as such does have some disagreeable traits. One should never eat anything green from a potato. The leaves and stem are poisonous.  
The greenish hue is actually chlorophyll, but it is also an indicator that an alkaloid, called solanine, may be present under the skin of the potato. Solanine develops in potatoes when they are stored in the presence of light (which also encourages chlorophyll formation) and either at very cold or quite warm temperatures. It is toxic, however it would take a very large number of green potatoes to make you ill. Since solanine collects just under the skin, it is safe to peel away the skin and a thin layer of white flesh before you cook the potato. And you're right about the sprouts: They too can be toxic and shouldn't be eaten, though it would take many sprouts to make you ill.
When confronted by green skin on a potato, simply peel it away. Keep as much of the rest of the skin as possible.
It's best to check potatoes for any green coloring before you buy them. Then, store them at cool room temperature in a dark, dry place.