Keratin and Langerhans cells 

The material on keratin and Langerhans cells got deleted somehow. I'd like to put it back in.  I think it's important because it explains a possible reason why circumcision might help protect against a number of diseases (in the case of keratin) and HIV in particular (in the case of Langerhans cells). Otherwise we're only presenting dry statistics. We can now cite a secondary source for this theory: the WHO document. I suggest the following:  "According to the WHO, the layer of keratin on the inner surface of the foreskin is thinner than on the shaft of the penis, which may make it easier for pathogens to enter, and cells targetted by HIV are also closer to the surface on the inner foreskin." (p. 13.)