TABLE 1.

Effect of formaldehyde on forward light scatter intensity and dry mass determined from flow cytometry and on Coulter Counter volume

Organism	Preservation time (days)	Forward light scatter intensitya	Apparent mean dry mass (pg/cell)b	Coulter Counter volume (μm3)
C. oligotrophus	0c	115	0.032	0.26
	0.1	159	0.038	0.26
	2	197	0.043	0.28
	49	200	0.044	0.28
E. coli	0c	7,363	0.383	1.13
	0.1	7,502	0.388	1.03
	2	7,245	0.379	1.10
	14	7,442	0.386	1.07
	49	8,427	0.413	1.08

^aMean intensity normalized with respect to the signal from the 0.6-μm internal standard. The value for E. coli has been multiplied by 0.8 to correct for the refractive index of the medium. 

^bDry mass computed from light scatter data with equation 6 of Koch et al. (37) and with K determined from the dry mass of C. oligotrophus. 

^cNo formaldehyde treatment.