International Standard Bible EncyclopediaBloody Sweat
(swet hosei thromboi haimatos): Described in Luke 22:44 as a physical accompaniment of our Lord's agony at Gethsemane (on the passage, which is absent in some manuscripts, see Westcott and Hort, The New Testament in Greek). Many old writers take this to mean that the perspiration dropped in the same manner as clots of blood drop from a wound, regarding the Greek word prefixed as expressing merely a comparison as in Matthew 28:3, where leukon hos chion means "white as snow." Cases of actual exudation of blood are described in several of the medieval accounts of stigmatization, and Lefebvre describes the occurrence of something similar in his account of Louise Lateau in 1870. For references to these cases see the article "Stigmatization" in Encyclopedia Britannica (11th edition), XXII, 550. It is perhaps in favor of the older interpretation that the word used by Aeschylus for drops of blood is stagon (Agam. 1122) and by Euripides stalagmos, not thromboi. None of the instances given by Tissot (Traite des nerfs, 279), or Schenck (Observ. med., III, 45:5), can be said to be unimpeachable; but as the agony of our Lord was unexampled in human experience, it is conceivable that it may have been attended with physical conditions of a unique nature.
Smith's Bible DictionaryBloody Sweat
One of the physical phenomena attending our Lord's agony in the garden of Gethsemane is described by St. Luke, (Luke 22:44) "His sweat was as it were great drops (lit. clots) of blood falling down to the ground." Of this malady, known in medical science by the term diapedesis , there have been examples recorded in both ancient and modern times. The cause assigned is generally violent mental emotion.