_Causes._ Like congestion this may be a result of =plethora= in overfed animals, in those subjected to specially stimulating food like gluten meal, cotton seed meal, beans, peas, vetches in excess, animal food for herbivora (the waste of hotels and restaurants for cows, compressed meat products for pigs), a period of absolute rest on full rations in horses habituated to hard work and full feeding; of =sexual over-stimulation= in males (stallion, bull, ram); of =violent overexertion=, especially if =under a hot sun=; of =sudden chill= when over-fatigued and perspiring; of =cold rain storms= (Freirier); of =rheumatism= (Kowalski); of =traumatism= (fractures, sprains, slipping with overdistension); of =falls upon the point of the ischium=; of blows upon the back (Cruzel, Trasbot); of =tumors implicating the cord=; of =too violent efforts in serving= by stallions; of =injuries of the great nerve trunks= passing off from the cord (Gull, Trasbot, etc.); of extensions from =caries or suppurations of the vertebræ= (Decoste, Trasbot); of =microbian infection=, as in rabies, distemper, tubercle, dourine, louping ill, milk sickness, contagious pneumonia, influenza, and suppurations; of =narcotic poisoning=, as from ergot, smut, the poisons of the cryptogams and bacteria of mouldy bread, musty fodder, spoiled meats, fish, etc.; also the poisons of =lolium=, =vetch=, =lupin=, =astragalus=, =oxytropis=, =arsenic=, etc. _Lesions._ These consist in a yellow or pink discoloration of the white and especially of the gray matter, and a special prominence of the puncta vasculosa in the affected part. Swelling or distortion of the part is not usual. This may involve only a single gray horn, the two horns on the same side, the two inferior horns, or all four at once, or the white matter adjacent may also show the rosy tint, the large puncta, and a characteristic softness and friability. Minute blood extravasations are very significant. Microscopically examined leucocytes are found in abundance in the perivascular spaces and in the neuroglia. The neurons (nerve ganglion cells) are degenerated, being cloudy, swollen, with enlarged nucleus, stain highly, and show enlargement of the chromophile granules. In a more advanced stage the cell has an indefinite outline and the nucleus is indistinct and may fail to take a stain; the chromophile granules are irregular and do not radiate evenly from a centre and many vacuoles appear. This may lead to fatty softening, or to fibrous increase of the neuroglia, and sclerosis.