While the Arabians were gradually rising by their power, intelligence, and renown, the Greeks were declining in inverse ratio; the genius, courage, and ancient virtues of the latter grew weaker and weaker, until they seemed on the verge of extinction. In the medical history of these centuries, in all Europe not under Moslem rule, there was but one man entitled to mention as an author in medicine,--viz., John Actuarius, the son of one Zacharia. He lived at the close of the thirteenth and the beginning of the fourteenth century; was employed at Constantinople, his surname being the honorary title of the court-physicians. He is more commonly known as Zacharia. Of his life we know little, save that he wrote several volumes, for the most part abridgments or commentaries on the doctrine of Galen. He laid great stress on the theory of critical days, and sustained his views by astronomical hypotheses most ingeniously combined. His was the first Greek work in which were mentioned the remedies introduced by the Arabians, yet he has not a word to say of variola, measles, spina ventosa, and other affections fully described by Arabic authors. He held remarkable views concerning the nature of man, whom he supposed to be formed by the union of two contrary substances,--the soul and the body; described somewhat elaborately an imaginary plexus of veins connected with the digestive{067} organs, through which the animal spirits were elaborated and purified; also, and quite methodically, for his age, he explained the functions of the animal economy and the etiology of disease.