Why do we say SOY milk?

[PJgunner]

My youngest daughter's son has a high allergic reaction to many foods. A glass of milk will darn near put him in the hospital, so all he can drink is soy milk. He can eat chicken and fish, but not beef, lamb or ham. I suppose there is place for that stuff, but I'm also thankful that it is there or the poor kid would just about starve to death.
Paul B.