Herophilus strove to supply one of the most conspicuous deficiencies in the Hippocratic system of medicine, viz., inadequate knowledge of the nervous system; and to this end he conducted a series of the most careful investigations, as a result of which he was successful in establishing several facts previously unknown. He described the membranes of the brain, the choroid plexus, the venous sinuses, the structure which bears his name,—the torcular Herophili,—the cerebral ventricles, and the calamus scriptorius; he traced the course of the nerve trunks for some distance from their origin in the brain and spinal cord; and it was he who established the fact that two different sets of nerves exist—one for conveying sensations to the brain and the other for producing motion. In addition, he investigated the corpus vitreum, the retina, the optic nerve, etc. He also called attention to the peculiar mode of construction of the duodenum, and to the fact that the walls of the arteries are thicker than those of the veins. Some idea of the accurate manner in which he carried on his anatomical researches may be gained from the fact that he noted the circumstance that the left vena spermatica occasionally originates in the vena renalis.
Herophilus also gained distinction in the practical branches of medicine. According to Puschmann he laid the foundations for a scientific sphygmography. Thus he distinguished several varieties of pulse in accordance with the differences which he noted in its strength, regularity, degree of fulness, and rate of speed. He also must have had considerable experience in surgery, as is shown by his remark that a dislocation of the thigh, owing to the tearing of the ligamentum teres which necessarily accompanies such a dislocation, is likely to occur again in the same individual. In his writings relating to the practice of medicine, Herophilus upheld the principle that experience alone should be our guide, as theoretical considerations are not to be trusted. He is also credited with having said, in response to the question, Whom do you consider the best physician? "Him who knows how to distinguish what is attainable from what is unattainable."
