Importance of a proper placement for your data point

To the Editor:I read the work by Hang et al.with much interest.This mighthave been a very important paper,which investigated the effectsof traumatic brain injury on the levels of brain-gut hormonevasoactive intestinal peptide (VIP),cholecystokinin (CCK),andcalcitonin gene-related peptide (CGRP) both in plasma and injejunum in rats.Some very clear-cut data were presented.I triedto compare their data with others reported in the literature,andfound that their data were unfortunately expressed in mass pervolume,i.e.,ng/L.This makes such comparisons impossible.