Please explain this in simpler words

Dear Student,

The above words were said by Evans when he was talking to the governor. Evans said the main problem was to prevent blood from hardening. He tells him that they got pig blood easily from a meat shop in Kidlington and said that one has to mix his own blood to stop it from hardening. Evans took a break and said that he mixed 3.8 percent of trisodium citrate to prevent it from clotting.

Regards