Symptoms are dependent upon species, size, location of bite and the amount of venom injected. Each protein possesses its own biological activity. The process by which a hemotoxin causes death is much slower than that of a neurotoxin. In the case of the three species of the Neotropical rattlesnakes Crotalus simus, C. culminatus and C. tzabcan recent research has revealed that their venoms can contain a neurotoxic component (crotoxin homologs), but is not always the case. Snake venom may vary in composition and toxicity across the geographic distribution of a species. See more. It is not known exactly how many proteins are present in a venom, but it probably consists of fifty to sixty components. Neurotoxin definition, a neurotoxic substance, as rattlesnake venom or the poison of a black widow spider. A further complication is that composition and activity of a snake venom vary among the species. Typically, a mammalian prey item will stop fleeing not because of death, but due to shock caused by the venomous bite. Snakes which envenomate a prey animal may have to track the prey as it flees. Snake venom is not composed of single compounds but is a complex mixture of proteins.