and on this site
http://www.bellaonline.com/articles/art9739.asp
Many pet owners don't realize that some of the mushrooms that grow in their yard are toxic to dogs and can even be fatal. Dogs who like to "graze" will sometimes eat wild mushrooms along with lawn grasses, leading to mushroom poisoning. Dogs can sometimes become ill by just licking a poisonous mushroom. Some dogs, like some people, are allergic to even edible, normally safe mushrooms. Symptoms of mushroom poisoning can range from mild vomiting and diarrhea to severe digestive problems to complete liver failure.
If your dog has eaten poisonous mushrooms...
If you catch him in the act - you actually see the dog starting to eat them....
Remove any pieces from the dog's mouth, and....
Induce vomiting with either -
Syrup of ipecac (1 teaspoonful per 10 pounds of body weight), or
Hydrogen Peroxide 3% - 1 tablespoon every 10 minutes, repeat 3 times.
Call your veterinarian.
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If your dog has eaten poisonous mushrooms, but there is short delay in realizing what has happened...
Save the specimens for identification.
Call your veterinarian or take your dog to a nearby emergency veterinary hospital immediately.
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If your dog has eaten poisonous mushrooms, and symptoms have already begun....
Take your dog to a nearby emergency veterinary hospital immediately.
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Protect Your Pets...
Always watch for mushrooms in areas where you walk your dogs or where they run and play. Be especially cautious of parasol-shaped mushrooms and all small brown mushrooms. Check your yard each morning, especially in damp weather, for new growth before letting your dog outside. Remember that new mushrooms can appear overnight. Whenever you find mushrooms in your yard, dig them up. Smashing or kicking them spreads the spores and even more will grow.
It can be very difficult to tell the difference between poisonous and edible mushrooms, and even harder to describe them over the telephone.
See the following sources for more information about poisonous mushrooms, including pictures to help identify them.