Answer : Protein
Explanation : When the scientist isolated the water soluble compound from the spider venom it had elements such as carbon,nitrogen, hydrogen and oxygen in its chemical structure this gives an assumption of the compound being a protein. But, further confirmation was given when it was injected under the mice skin and which broke down the structural materials in the cell membrane, this is one of the property of protein. And he is going to find out about its toxicity to humans.