In Ray Bradbury's Fahrenheit 451, how does the conversation about "the age of disposable tissue" (from Clarisse's house) relate to the events in Montag's house a few moments earlier?
I teach a media studies class to high school students at the school where I teach. I have a unit on myths of American culture. One of the myths that we study is called the "Myth of Endless Abundance." There are several layers to it, but I define it for my students as follows:
We [America] possess more than we can ever use. America is a land of such overwhelming natural resources and productive potential that we will NEVER run out of anything essential to comfort and well-being.
Regardless of whether or not the myth is actually true or not is irrelevant. All that matters is that the majority of Americans believe it. And there is no doubt that we believe it. Nobody ever questions whether or not there will actually be gas available at the pump. Nobody wonders if the grocery story will have fresh vegetables and dozens of cereals. Nobody worries about throwing out paper plates and napkins, because they know that they can always get replacements. If I drop my cell phone down the toilet, I'm upset at myself, but I don't doubt that I can get another one. Verizon won't tell me "sorry buddy, all out of phones."
The quote that your question mentions is along the lines of endless abundance. The people speaking at the McClellan household make the comment that they live in the age of disposable tissues. But the quote isn't referring only to simple bathroom tissue. It is referring to real, living human tissues. Moments before Mildred was as good as dead, because she overdosed on some kind of drug. A pair of "handymen" showed up and pumped out the toxins from her stomach and blood, and then they pumped in new, healthy blood.
This machine pumped all of the blood from the body and replaced it with fresh blood and serum.
The men working on Mildred aren't even doctors. In fact, they laugh at Montag for even mentioning it. The job that they just performed has grown so commonplace that they are essentially plumbers responding to nearly ten calls per night.
"Hell! " the operator's cigarette moved on his lips. "We get these cases nine or ten a night. Got so many, starting a few years ago, we had the special machines built.
Their job of replacing human tissues with such relative ease shows that the people in Montag's society not only think their household items are endlessly abundant, but they also think that their living tissues are endlessly abundant as well--so much so that the people don't worry too much about damaging their own tissues.
After Millie Montag gets her stomach pumped and her blood replaced, Guy leaves the house and goes over to the McClellans' home. He hears the words you mention. To me, they apply to what has just happened at his house in a couple of ways.
First, something that was part of Millie has just become, quite literally, disposable. The men are taking away Millie's blood (as well as the contents of her stomach) and will presumably throw it away. This shows how much people have lost their humanity -- their very blood has become disposable.
Second, you can say that Millie herself is disposable. It's like she does not even care about herself anymore. She no longer thinks of herself as something important.