READing JournaL !!!!!!!

HEEELLLLLLLLOOOO EEEEVVEEERRRYYYOONNEEE:]
OK so for those who don't know I'm still currently reading The Witches by Roald Dahl.
In this book i am currently at the part where his grandmother buys him to mouses and they are taking vacation in the hotel.In the hotel the manager tries to take the boys mouses so the grandmother blackmails him.The boy can take the mouses out of the cage so he is finding a new place to train them at.

The quote i chose was "Its Tommy rot.But just for once I think we've got to obey the doctor."
I chose this quote because i was curious of the meaning. Like What is tommyrot? And why do they have to listen to the doctor?This quote was at the part of the book when grandmother got sick and then recovered so that she could take her grandson on a trip to Norway. I think the doctor said she couldnt go for her on health but it still sucks because It would have been good for the boy to go out especially after his parents just died:[