aerosol A particle (made of any material of any density) that is small enough and in the correct shape (usually round, but not necessarily so) so that it remains buoyant in the atmosphere without external energy to keep it aloft. From a functional standpoint, an aerosol particle behaves essentially “like the air itself.”
In the context of disease, infectious particles that behave as aerosols (e.g., the influenza virus expelled during a cough or a sneeze) can spread long distances—many hundreds of feet or even miles—and infect other susceptible hosts. As a result, much of the research in biological weapons programs—both legal “defensive” and illegal “offensive” programs—is focused on the generation of aerosols and engineering organisms that can sustain the processes by which they can be converted into aerosols.
Some organisms (e.g., the bacteria that cause tularemia) appear to aerosolize naturally whereas others (e.g., pneumococcus) do not, at least under typical environmental conditions. As a general rule of thumb, in order for infectious particles to behave as aerosols, their size must be in the range of 2–8 microns (millionths of a meter) in diameter.
Alzheimer's disease A poorly understood degenerative disease of the human brain leading to memory loss, personality changes, and dementia, and ultimately ending in death. The cause of Alzheimer's disease is unknown, but based on the best scientific evidence to date, it is not due to a disease-causing protein orprion (q.v.).
amino acid The basic chemical constituent of proteins. Multiple amino acids strung together are, by definition, a protein. About 20 amino acids are found in most of the proteins that make up life on earth. Some examples of amino acids are well known to those who purchase them as dietary supplements: tryptophan, lysine, arginine, etc. A small subset of amino acids (e.g., valine, phenylalanine, tryptophan, lysine, and histidine) are called “essential” amino acids because they cannot be syn