Biomedical Ephemera, or: A Frog for Your Boils

Bilharziosis Roundworm -Schistosomum haematobium

For all the awful things bilharziosis (or schistosomiasis, depending on your region of the world) does, their reproduction is almost endearing. The female is a "normal", worm-like shape, but the male is shaped almost like a boat or trough. Once the nematodes reach adulthood, they seek out another of their kind (as they can only reproduce sexually), and pair up. Once paired up, the female nestles into the trough of the male, and the male takes over feeding for both of them. Though they never fully merge (like the anglerfish male does with the female), they can remain together for years, with the female producing their eggs, and the male feeding them both. It's almost cute.

Bilharziosis. Frank Cole Madden, 1907.

Venereal disease is rarely limited to the sexual organs when it's not treated...

A. Late eczematoid syphilide of the leg showing mushroom-like nodules.

B. A late papulo-squamous syphilide resembling the heaped-up scales of a chronic psoriasis.

C. Leucoplakia of the tongue.

Dermatographia [dermatographic uticaria].

About 4-5% of the population have what's commonly known as "skin writing". The root causes aren't fully known (though it's suspected to have multiple causes, including nutritional problems and stress reactions), but it occurs when the skin has an allergic-type reaction to any form of scratching or rubbing of the skin, even though it's not reacting to any antigens. The affected area is generally itchy or somewhat burning, but not very painful. The condition also does not cause a generalized allergic reaction, except for in about 50% of first outbreaks (reasons for that are unknown). 

Swelling and redness generally disappear within 15-30 minutes, but sometimes last for hours.

A Practical Treatise on Diseases of the Skin. James Nevins Hyde, 1909.