Re: Virus vs Bacteria
It was just a story.
However most poison by products of a bacteria might be generally toxic, like hydrogen cyanide.
The blood might have proteins, fat, glucose etc, probably generally utilisable. Blood can be used as a fertiliser for plants. It's mostly water. The main thing after that is protein. Low in fat and sugars. Some vitamins (possibly no use to aliens).
Blood is the only animal product mentioned in the bible forbidden to Noah (not Jewish), Jews and Christians of Gentile origin in the book of Acts (No doubt because of the Covenant with Noah). "The life is in the blood".
I've no idea why H.G. Wells picked blood. Curiously the ships mentioned were already obsolete when he wrote the story (1897).
"The quick pace of change meant that many ships were obsolete as soon as they were finished, and that naval tactics were in a state of flux. Many ironclads were built to make use of the ram or the torpedo, which a number of naval designers considered the important weapons of naval combat. There is no clear end to the ironclad period, but towards the end of the 1890s the term ironclad dropped out of use. New ships were increasingly constructed to a standard pattern and designated battleships or armored cruisers." — Wikipedia. Also stated elsewhere.