Because the article did not draw that distinction, but it did draw that distinction for other observations. Specifically the more general observation was stated

Because the article did not draw that distinction, but it did draw that distinction for other observations. Specifically the more general observation was stated more generally (white blood cell activity discovered to be region specific), and scoped more specific claims to be 'in mice' (and these drugs target specific regions). But to be blunt it seems like your query would be best resolved by looking into the history of rodents as lab animals for preliminary medical studies. I cannot give you a robust account, if google fails I recommend asking a librarian for help or contacting people who have published on the topic. Do not fear impinging, I think for many it is an opportunity to share a special interest with an interested third party (a rare treat).