After crawling through the Jeffries tube, Captain Janeway scans Neelix, telling him he has high fever and fluid in his lungs. He replies: "Lung." Both of Neelix's lungs were removed by Vidiians in Phage (1995), and he subsequently received a single lung in a transplant, donated by Kes.
Macrocosm bears thematic resemblance to Alien (1979). The Captain finds herself acting as a Ripley character, combating an alien that uses human hosts to multiply, and crawling through the tubes of the ship fighting the Alien infection with a large weapon.
Introduction of a new alien species, the Tak Tak, to the Star Trek universe.
When scanning the residue left by the perpetrator, Janeway says that it is some sort of "mucilaginous compound"; mucilage is a thick, viscous substance produced by plants and some microorganisms. Plants use mucilage to store food and water and it also plays a role in seed production and germination. In micro-organics it is used as a form of locomotion; some microorganisms, namely protists like algae and amoeba, secrete the fluid to propel themselves forward.
47 reference: after beaming down to the Garan mining colony, the Doctor proceeds on vector 1-4-7.