We learn about Rocky’s unique immune system in chapter 24 when Ryland asks if Eridians have diseases. Rocky replies that Eridians defend themselves from diseases by having bodies that remain completely closed to the outside environment except when eating, laying an egg, or after sustaining a wound. Once the opening in the Eridian body reseals, they use their hot circulatory system to kill diseases (for more on the two circulatory systems of this species, see #150).

Ryland reflects on the effective multi-purpose Eridian circulatory system and determines that it makes sense: “If any pathogens do get in, the body seals the area off and boils it.” 24.098 Of course, human immune systems have a few more players at the table, but our bodies do use heat to defend us from infection by pathogens.

Fever is a defense mechanism regulated by the hypothalamus which can trigger higher-than-normal temperatures in the body as a response to infection. Fever as an immune response has existed for over 600 million years of evolution in both warm and cold-blooded vertebrates, as well as in some invertebrates.

While fever does directly induce stress on invading pathogens, it also works to bolster other aspects of immune response. An increase in body temperature has been shown to benefit lymphocyte activation and neutrophil migration, augmenting the performance of these vital immune cells.

Rocky may have an impressively straightforward heat-based immune response, but given the “borderless police state” 24.099 of the human body, we need all the help we can get.