Chromatolysis and axonal dystrophy in the autonomic nervous system in grass sickness of equidaeLight and electron microscopic examinations of autonomic ganglia from cases of grass sickness have been carried out. The main alterations are pyknosis, cytoplasmic vacuolation originating from granular endoplasmic reticulum, and axonal dystrophy. The cell body changes bear some resemblance to chromatolysis. OBEL A-L. (1955) Studies on grass disease. The morphological picture with special reference to the vegetative nervous system. Journal of Comparative Pathology 65, 334-346 of horses with and without grass sickness. British Veterinary Journal 130, 265-270 analysis. Journal of Comparative Neurology 132, 18S212 and dystrophic axons.