Go to amazon.com and type in venemous snakes or venom. There are TONS of book that come up that specifically deal with snake and animal venoms, affects on the body and WHY the body react to venom a certain way. People who inject them selfs with venom do so not to become resistant but because their bodies "memory cells" i guess youd call them dont recognise venom a second time and they dont build the antibodies. People get sick the first time they are bitten because they have no antibodies agaisnt the venom. After the second bite your body is suppose to recognise the venom and since u have anti bodies the effects of the venom arent usually servere.
But...check out some books. there are at least 3 really good ones on amazon.com.