But Cayce never said that psoriasis is contagious. Read in context, Cayce seemed to be using "infectious" to mean "can affect."
"Seemed"? Not good enough.
Prove it.
And while you're asserting that Cayce's use of any word need not necessarily correspond to the commonly understood meaning of that word, and that we can therefore discard the dictionary in the context of this thread, you can also prove that
any word or concept Cayce ever used meant what it is commonly understood to mean. You can start by proving that "14,000" actually means "14,000" in Cayce-speak, and not, say, "30,000."
But what causes the immune system to do something other than what it is supposed to do?
The "unknown stimuli" mentioned in the UMDNJ bit you quoted earlier. These cause the immune system to malfunction, and produce the collection of symptoms which are known as psoriasis. The malfunctioning of the immune system is the
cause, psoriasis is the
effect. By stating that "psoriasis is an infectious condition that affects the emunctory and lymph circulation," Cayce is claiming that psoriasis is the cause, not the effect.
"Generalized pustular psoriasis can make life-threatening demands on the heart and kidneys."
Fascinating. Of course, this does not apply to psoriasis generally, or even to pustular psoriasis, but specifically to Von Zumbusch pustular psoriasis. As
the NPF website states:
Von Zumbusch pustular psoriasis is associated with fever, chills, severe itching, dehydration, a rapid pulse rate, exhaustion, anemia, weight loss and muscle weakness.
From the text of reading 943-17, it appears that the subject was suffering from simple plaque psoriasis; almost certainly not from Von Zumbusch pustular psoriasis, as he makes no mention of anyhting that could be interpreted as indicating one or more of the quoted symptoms. Even if he were, though, Cayce's recommendations to the subject would do nothing to help, and would likely be counterproductive.
What proof do you have that these statements are incorrect?
Simply that Cayce made numerous statements, all of which contradicted other statements he made. So even if (and that's a very big "if") he was right some of the time, he must, logically, have been wrong the rest of the time. As it happens, the statement from reading 943-17 you have chosen to defend is the one of the few times Cayce claims that psoriasis is the cause, rather than the effect of the underlying disorder ("psoriasis is - itself - an infectious condition that
affects the emunctory and lymph circulation, and
causes an improper coordination of the eliminating forces of the system"), you've in effect conceded that Cayce was,
at best, wrong way more often than he was right.
And what was the source for Cayce's medical knowledge?
You mean the lack thereof. Who knows? Given how spectacularly wrong he was, even by the standards of the time, we can safely eliminate even contemporary medical science, and certainly any psychic ability. Other than that, we can only speculate; old wives' tales, perhaps, or a cursory reading of medical texts predating the germ theory of disease, stuff he pulled out of his arse, or a combination of the aforegoing. The only thing we can be certain of is that he had no actual understanding of what he was on about.
but you still haven't shown that Cayce's psoriasis treatment doesn't work. No, that doesn't mean it does work, but that's completely different than it having been debunked. I would also note the following quote from noted psoriasis researcher Alice Gottlieb: "Ten years ago, research on the pathogenesis of psoriasis focused primarily on affected skin cells. Today, its primary focus is the immune system." See -- 
