> I mean whether someone dies from poison depends on their immunity system, not just how much they're given.
According to my research, including the [CDC](
emergency.cdc.gov/agent/ricin/qa.asp) and the [NIH](
ncbi.nlm.nih.gov/m/pubmed/14579547/?i=3&from=/8119491/related) it doesn’t seem to me that ricin is at all affected by the immune system, other than a very rare natural immunity some people have. So a chemist with half of Walt’s experience (hell one with half a college education) would be able to calculate a non-lethal dose likely just with the weight of the patient.
More importantly, it’s pretty intuitive that Brock ate the poison as opposed to other methods of ingestion. This quote is pulled from this breaking bad fandom page for ricin: “Ingesting ricin is much less lethal, requiring on the order of 30-40 mg per kilogram. By ingestion, the pathology of ricin is largely restricted to the gastrointestinal tract where it may cause mucosal injuries; with appropriate treatment, most patients will make a full recovery.” This info is extremely helpful because it’s clear that a non-lethal oral dose of ricin could easily be calculated with a LOT of room for error.
However, I may be remembering incorrectly but it wasn’t clear whether Lily of The Valley or ricin was the poison of choice in this situation. While a non-lethal dose of concentrated ricin in this situation may be easy for a chemist to calculate, botanicals complicate things. There are ~40 unique toxins in LotV, and each plant is going to vary in concentration and possibly presence of each of these toxins (think like cbd and thc in weed). Unless Walt did some real work on extracting, identifying and quantifying the toxins in his specific sample of LotV, proper non-lethal dosage calculations would be purely educated guesswork.
So if Walt used ricin to poison Brock, there is absolutely no reason to expect Walt to not dose him ‘properly’. Anything else would be sloppy chemistry which is one thing Heisenberg doesn’t do. However if he went for the LotV, it would be very very difficult or maybe impossible for Walt to dose correctly without tons of behind the scenes chemistry going on. IMO it could go either way; if he used LotV then I agree with the sentiment that at that point he saw Brock (thus basically all other children/people other than his loved ones) as expendable consciously. However, if he opted for the ricin, I think that’s more of the same theme of “I’m the greatest chemist of all time I can do anything” so more speaking to his ego as opposed to anything else
[Sorry it’s been a while since I watched the show, so I could have gotten some BB specific details wrong]