The idea that the Voynich manuscript is a medical text seems plausible, but the theory that it uses a logographic representation (one symbol per word) rather than an alphabetic or even a syllabaric (one symbol per syllable) one seems less likely to me. A cursory examination of the manuscript (http://www.voynich.nu/folios.html) reveals that the lexicography looks much more like an alphabetic encoding than a logographic one like Chinese. The symbols are collected into word-like groups separated by white space. Also, it appears that there are too many repeated symbols and insufficiently many distinct symbols for a logographic language.