I think one way that the narrator contrasts the Anarchist and the Bacteriologist is by focusing quite a bit on the Anarchist's physical traits. We are told repeatedly that the Anarchist is pale-faced. A bit later we get a great sentence that talks about his hair color and some other physical traits.
The lank black hair and deep grey eyes, the haggard expression and nervous manner, the fitful yet keen interest of his visitor were a novel change from the phlegmatic deliberations of the ordinary scientific worker with whom the Bacteriologist chiefly associated.
The black hair has to stand out against such a pale face, but the overall image being created seems to be one of a sickly looking individual. We don't get this kind of narration about the Bacteriologist. We hear him talk and can listen to some of his thoughts, but he really doesn't get a physical image until he starts running after the Anarchist. Once that happens, the narration tends to focus on how silly the scientist looks.
The Bacteriologist, hatless, and in his carpet slippers, was running and gesticulating wildly towards this group. One slipper came off, but he did not wait for it.
The two men are similar in that they are smart enough to recognize the potential threat and danger of small biological microbes to the world. They are both fascinated with the power of such a small organism.
"Once start him at the water supply, and before we could ring him in, and catch him again, he would have decimated the metropolis."
Unfortunately, the scientist is naive about it. He can imagine the destruction, but he can't fathom somebody actually wanting to do it.