My friend's grandfather was granted exemption from conscription in the last couple of years of WW1, although he did have to keep reapplying. The reason given was that he was classed as C3. The newspaper report of his being granted exemption reads that he was "a cotton cloth-looker (sedentary work at home), single C3". I have discovered that this would have been something to do with a medical condition, but I can't find what sort of condition this might be. Any ideas?