plants in hospitals

Charles Delwiche delwiche at
Thu Oct 22 17:48:07 EST 1992

In article <9210220058.AA12163 at> preissj at CLVAX1.CL.MSU.EDU ("J Preiss--Seq Anal") writes:
>        I had heard this same thing about 30 years ago and was certain that a 
>modicum of reality had prevailed to eliminate the patent silliness. I am not 
>sure, but I would bet that this assertion arose shortly after the  
>demonstration of the light-dependence of CO2 fixation with the concomitant 
>constitutive nature of respiration. The state of medicinal practice was less 
>than pathetic, and physicians, in an effort to seem "scientific",  sought 
>"causes" of their failures.

Jan Ingenhousz, in his seminal work on photsynthesis _Experiments Upon
Vegetables_  (1779,  P. Elmsly in the Strand, London) wrote in section
XVII "On the Effect of Leaving Plants Kept in a Room":

	Though I think, that the keeping of a few plants in rooms is
	very indifferent as to the health of the persons who live in
	them; yet it is not so indifferent for us to know the effects
	which plants have in reality on the air of the room, that we
	may avoid danger from any excess.

	The influence of plants on the air of a room in which they are
	kept is different in the night from what it is in the day.  In
	the day plants are apt to contribute somewhat to purify the
	air of the room, if they are placed so as to receive all the
	light of the sun possible: if they are placed so as not to
	receive the direct influence of the sun, but to be free from
	any shade, they seem to have no influence at all, either in
	improving the air of the room or in fouling it.  [text
	omitted] But I remember to have found several orange trees in
	a room, by way of ornament, and, as I were told, to keep the
	air of the room wholesome: I think now such ornamental plants
	by no means indifferent, unless they were but small and the
	room ample; at any rate I should not suffer them to be kept in
	a room at night, where a sick person is.

	H. S. Reed, "Jan Ingenhousz, Plant Phsiologist, with a history
	of the discovery of photosynthesis"  _Chron. Bot. 11: 285 - 396.

I would say that J. Preiss hit pretty close to the truth.  Ingenhousz
was physician, but was also interested in plant physiology and is
credited with having discovered the basic chemical processes
underlying photosynthesis.  Before we bash 18th century physicians too
hard, we should remember that Ingenhousz was working at a time before
it was understood that oxygen was consumed during burning, and it was
instead believed that a fire quenching substance "phlogiston" was
produced.  Phlogiston is, in effect, the inverse of oxygen.  It was
known that animals would suffocate, and this was attributed to an
accumulation of phlogiston.  Air with a high concentration of
phlogiston (i.e. low concentration of oxygen) was considered to be
"unwholesome" or "injurious".  

Ingenhousz discovered that plants released gas, and that in the
process they "purified" unbreathable air.  This leads to some great
chapter headings in "Experiments Upon Vegetables": "The
dephlogisticated air oozing out of the leaves in the water is not air
from the water itself", or "Flowers ooze out by day and night an
unwholesome air".  My personal favorite is: "Some remarks on the green
matter which settles at the bottom and sides of the jars in which
water is left standing", but I just like that because I study algae.

I don't have any opinions about whether or not plants are a problem in
hospital rooms, although I admit scepticism.  I do agree with the
sentiment, previously expressed on the net, that it would be nice to
try to actually measure CO2 and O2 levels in a room with a few house
plants and see how much the CO2 levels varied (since the atmosphere is
20% oxygen I doubt very much that oxygen levels would vary
measurably).  It should also be noted that plants release trace gasses
as well, which might be good or bad, and have also been shown to
accumulate particles from the air, I think just by an electrostatic
effect, so there *could* be some effects not related to CO2 or oxygen.

At any rate, the belief that house plants could be a problem in a
hospital room runs right back to the initial elucidation of
photosynthesis, and I wonder if anyone since Ingenhousz has really
studied the matter.  I think it is also fair to point out that
Ingenhousz himself didn't think that it was any big deal.

Charles F. Delwiche			(812) 855-2549
Dept. of Biology, Indiana University
Bloomington, IN 47405

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