Via IFL Science:

Herpetologist Dr. Karl P. Schmidt in 1957 was bitten by a snake from the Chicago Zoo he had been trying to identify. The snake proved to be an example of Dispholidus typus, the Boomslang.

The snake was a juvenile example, and Dr. Schmidt believed it was not capable of delivering a lethal dose of venom. In any event, there was no Boomslang anti-venom available in Chicago, so Dr. Schmidt did not seek medical treatment initially. He merely commenced a diary, noting the effects of the bite and his personal movements and response, before he collapsed and died the following day.