Curses, you've made me break my "No HN on my work computer" anti-procrastination method. At least it's been only 15 minutes though.

Direct link to the research: http://www.gwern.net/docs/algernon/1995-rechtschaffen.pdf

The paper is titled "Sleep deprivation in the rat by the disk-over-water method." As the name implies, rats are suspended on a disk over water. They can't fall asleep without starting to drown. Thus they are kept awake.

The paper begins with, "Because short-term sleep deprivation (SD) may stimulate
only sleep-promoting mechanisms, chronic SD may be
required to elicit function-revealing deficits. However, the
enforcement of chronic SD requires repeated, intrusive
stimulation which can blur the interpretation of effects. Do
they result from sleep loss or from the strong stimulation
used to enforce SD? To simplify communication, we speak
of the 'effects' of SD, but strictly speaking, SD studies are
correlational. We apply stimuli to enforce SD and report
the relationship between the ensuing sleep loss and
changes in performance or physiology. However, the
changes and the sleep loss could be independent responses
to the stimulation. The interpretation that the changes
result from sleep loss hinges on minimizing the contribu-
tion of the deprivation-enforcing stimulation, which can be
especially difficult when strong stimulation is used to en-
force chronic SD."

There are two possibilities. Either rats being repeatedly almost-drowned doesn't contribute to death after 45 days, or it does. The paper goes on to demonstrate the steps they took to minimize the chance that almost-drowning rats resulted in death:

"Hypothermia had been suspected as a proximal cause
of death [3,31,34] because all SD rats showed an eventual
decline in intraperitoneal temperature (Tip); a decline to
more than 1 °C below baseline in otherwise untreated SD
rats has been a reliable indicator of impending death within
a day or two. However, TSD rats kept warm by exogen-
ous heating died nevertheless"

"A second possible cause of death is breakdown of body
tissues due to catabolism, secondary to the high metabolic
rate in TSD rats [3,14,31]. [...] Evidence against catabolism as a mediator of preterminal
effects includes a lack of preterminal serum albumin de-
cline in PSD rats [22] and the deaths of all rats in two
TSD groups protected against catabolic effects, hypothy-
roid rats and high-calorie diet rats. Thus tissue breakdown
secondary to catabolism was not a necessary cause of
death."

However, this third point is a key conflating factor:

"A third major candidate for proximal cause of death is
organ failure secondary to systemic infection, as suggested
by bacteremia, which Everson has observed in five of six
TSD rats obviously near death [11]. We subsequently
confirmed bacteremia in two additional preterminal TSD
rats [20]. Very recently, we treated six TSD rats with
antibiotic cocktails; five progressed to an apparently ter-
minal condition nevertheless and were then killed (after
10-16 days of TSD). Neither heart blood samples, livers,
kidneys, nor mesenteric lymph nodes showed aerobic bac-
terial or fungal infection. The sixth rat died after 19 days;
blood could not be drawn, but the other tissues were har-
vested shortly thereafter and were also free of aerobic
bacteria and fungi. These results indicate that microbial
invasion is not a necessary cause of death in TSD rats."

If you read carefully, they begin by saying "almost-drowning rats eventually results in organ failure." They end with "microbial invasion is not a necessary cause of death."

I think it's possible that almost-drowning rats causes organ failure for reasons other than microbial infection. The fact that the rats progressed to a terminal condition even after antibiotics seems to support this hypothesis. Their organs failed anyway. I wonder if dunking them in water for a month had something to do with it, and not the sleep deprivation?

The paper seems to tiptoe around this point.