I remember the testing for TB in school back in the 1960's. The "jelly test" was the original way but then it was a circular multi point injection. In both cases if the area was "raised" after a few days it indicated you had been in contact with a TB sufferer & probably had a built in immunity. You were then sent for a chest x-ray
No raising & you had to have the TB jab. I watched several of my class faint while having it