Reading an interesting post at Genomes Unzipped, “Human genetics is microbial genomics“, which states:
Only 10% of cells on your “human” body are human anyway, the rest are microbial.
Have you read a sentence like that before? So have I. So has a reader who left a comment:
I was wondering if you have a source for “Only 10% of cells on your “human” body are human anyway, the rest are microbial”
It’s a good question. Everyone quotes this figure, almost no-one provides a reference. Let’s go in search of one.
Wikipedia. Don’t make it your primary source. However, it’s often a good place to start. From the human microbiome article:
Bacterial cells are much smaller than human cells, and there are at least ten times as many bacteria as human cells in the body (approximately 1014 versus 1013). 
Reference : Berg, RD (1996). The indigenous gastrointestinal microflora. Trends Microbiol. 4 (11): 430–435. If you have access to the full text, you’ll find a PDF which seems to be a poor-quality scan of the printed article. From page 432:
In summary, there are ten viable indigenous bacteria in the GI tract for every cell in the human body: 1013 total GI bacteria compared with 1012 total cells making up the human body.
Note the order of magnitude differences compared with the Wikipedia article. I was unable to find a reference in this article to any paper where these numbers were measured or estimated. And so…
…reference : Savage, DC (1977). Microbial Ecology of the Gastrointestinal Tract. Ann. Rev. Microbiol. 31: 107-133.
Another PDF so old that we cannot copy/paste from it. The opening sentences:
The adult human organism is said to be composed of approximately 1013 eukaryotic animal cells (27). That statement is only an expression of a particular point of view. The various body surfaces and the gastrointestinal canals of humans may be colonized by as many
as 1014 indigenous prokaryotic and eukaryotic microbial cells (70).
Note the order of magnitude discrepancies compared with the previous article.
Reference (27) is: Dobzhansky, T. (1971). Genetics of the Evolutionary Process, Vol. 1. New York: Columbia Univ. We’ll leave that one there.
Reference (70) is: Luckey, TD (1972). Am. J. Clin. Nutr. 25: 1292-95. Time to search PubMed:
luckey td[au] 1972[dp]
Hey look, another ancient PDF – and the last page is 1294, not 1295. First page, second paragraph:
The composition of this system is surprising. Adult man carries 1012 microbes associated with his epidermis and 1014 microbes in his alimentary tract (Fig. 1). The latter number is based upon 1011 microbes/g contents of an alimentary tract with a capacity of approximately 1 liter. The 1013 cells (2) in his body are a distinct numerical minority of the total being that we call man. If we abandon anthropomorphism for the microbic view, we must admire the efficiency of these microbes in using man as a vehicle to further their own cause.
This would seem to be the “definitive” reference, for now. Reference (2) in that quote is Dobzhansky, again.
No mention of adult woman. It’s OK, that’s just how people spoke and wrote in the 1970s.