Saturday, October 11, 2003

He copied me! Ok so he did more work on it and had more info, and did a better job of it...but that's beside the point. As for condoms being unable to prevent the passage of HIV - [can't find the research now, so please forgive the ill-described science] I think the individual virus in it's dormant carrier form (ie the traditional image of a virus), is quite a bit smaller than the latex molecules, and smaller than the gaps between the molecules. However in normal use the virus is contained within a water based fluid and so is pretty hydrophilic. Latex is hydrophobic, so water and most structures suspended within it will not easily leave to interact with the latex. So either the virus would have to leave a hydrophilic environment and pass over the surface of a series of hydrophobic molecules, or it would have to leave the fluid for air, which would take quite a bit of energy (and I'm not aware of HIV acting as an airborne disease). So if the virus escapes the ejaculate and reaches the outside surface of the condom then it would have to pass into another hydrophilic environment (the recipient’s body). But this would mean the virus would have to go from hydrophilic, to hydrophobic, and back to hydrophilic, which would require energy expenditure to either do this chemically or by more mechanical means. Which given that the viruses borrow the host cell's equipment normally, and that the infective virus in the ejaculate is in the dormant state [i.e. it is pretty much only data, and it's not connected to a cell], rather limits this occurrence. So the virus lacks the means of changing that would allow it to pass. But could it by benign forces alone? Not really, as the innate hydrophilia or hydrophobia of a structure means that on meeting an interface between the two phases (eg water and latex), the structure will bond best with the environment that best reflects it's characteristics. But there is a second interface, the reverse of the first, so either the structure (e.g. virus) will not have passed in the middle region, and thus be stuck in the original substrate (the ejaculate), or it will have passed into the middle (the latex). But if the structure reacted better with the middle substrate than the first, it will also react better with that than the last (bodily fluids being fairly similar), and so will not pass beyond the middle substrate. This is the same mechanism that our cells use to keep the contents separate from the outside.

So while it is technically possible for HIV to pass through a condom, it is pretty improbable. Although latex does allow things like very small molecules to pass through, such as acetone, but that's because it's really small (well relatively), and has both hydrophilic and hydrophobic ends.

Sorry for the really bad presentation (see now this is why pictures/diagrams are useful), but I blame it on (well apart for never being able to write coherently - there's always too many exceptions and provisos, and not enough paragraphs) waking up sometime before 4am, knowing I've got to ferry my parents to Waterloo by 6:30ish, and then coming back during dawn. So I've forgotten where I put reality.

And isn't it handy that a train service that usually takes 45mins, takes 1hr 20 on Saturday mornings and the earliest doesn't get in to London till 7am. And Eurostar insist on people being there 45mins before the train, which is at 7:20. So somehow it got arranged that we'd go up at 5:30, and then having dropped them off I'd come back again. Except this being this family, we didn't leave till about five to six, so we got there about the same time as the first train would have done. And my father managed to get flashed by a speed camera (but only once?), doing 50 in a 50 limit. Go figure.

And Skodas don't do acceleration. It didn't help that the rev counter is where my speedo is and vice versa. And it only has 20 and 40 visibly marked. And as it's fairly new nothing reacts when you touch it, as all the pedals just flop about, instead of needing your whole body weight to move them (makes parking easier though). But it doesn't have any notches where it just settles at one speed, so it always seems like it's in too high a gear (even in 1st). But doesn't have a leak and accompanying mould, has a radio and power steering (it's no fun when it doesn't feel like you're hoisting the car into the space).

And does anyone drive in bus lanes even when they're not in force? Other than the black BMWs and silver Mercs who always do far more at least 30mph more than you.

Hmm, tiredness is not good. And I better go and find some lunch.

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