Microglia
Research has discovered dystrophic (defective development) human microglia. "These cells are characterized by abnormalities in their cytoplasmic structure, such as deramified, atrophic, fragmented or unusually tortuous processes, frequently bearing spheroidal or bulbous swellings." The incidence of dystrophic microglia increases with aging. Microglial degeneration and death have been reported in research on Prion disease, Schizophrenia and Alzheimer's disease, indicating that microglial deterioration might be involved in neurodegenerative diseases. A complication of this theory is the fact that it is difficult to distinguish between "activated" and "dystrophic" microglia in the human brain.
History of model organisms
Insects were not the only organisms entering the laboratories as test subjects. Bacteria had also been introduced and with the invention of the electron microscope in 1931 by Ernst Ruska, a whole new field of microbiology was born. This invention allowed microbiologists to see objects that were far too small to be seen by any light microscope and thus viruses which had perplexed biologists of many fields for years, now came under scientific scrutiny. In 1932 Wendell Stanley began a direct competition with Carl G. Vinson to be the first to completely isolate the Tobacco Mosaic Virus, a virus that had been until then invisibly killing tobacco plants across England. It was Stanley who would accomplish this task first by changing the pH to one a more acidic one. In doing so he was able to conclude that the virus was either a protein or closely related to one, thus benefiting experimental research.