This Chapter XI. is an important one. Harvey takes the operation of bleeding as one which is familiar to every class of his readers, and he uses the various phenomena which attend the application of a ligature to the arm to clinch his arguments as to the existence of the circulation of the blood. He introduces incidentally his surgical and pathological knowledge, quoting, amongst other instances, the fact that if the blood supply to a tumour or organ be stopped, "the tissues deprived of nutriment and heat dwindle, die, and finally drop off." He also introduces some pathological results from personal experience, for he says:--"Thrown from a carriage upon one occasion, I struck my forehead a blow upon the place where a twig of the artery advances from the temple, and immediately, within the time when twenty beats could have been made, I felt a tumour the size of an egg developed, without either heat or any great pain; the near vicinity of the artery had caused the blood to be effused into the bruised part with unusual force and velocity." This passage shows one of the minor difficulties that Harvey and all observers in his age had to contend with in the fact that no method existed by which small fractions of time could be measured.[11] The ordinary watch had only a single hand marking the hours, so that neither minutes nor seconds could be registered by them. The difficulty was one of old standing, and Dr. Norman Moore alluded to it, when he says in regard to Mirfeld's "Breviarium Bartholomei:" "The mixture of prayers with pharmacy seems odd to us; but let it be remembered that Mirfeld wrote in a religious house, that clocks were scarce, and that in that age and place time might not inappropriately be measured by the minutes required for the repetition of so many verses of Scripture or so many prayers. Thus Mirfeld recommends that chronic rheumatism should be treated by rubbing the part with olive oil. This was to be prepared with ceremony. It was to be put into a clean vessel while the preparer made the sign of the cross and said the Lord's Prayer and an Ave Maria. When the vessel was put to the fire the Psalm 'Why do the heathen rage' was to be said as far as the verse, 'Desire of Me, and I shall give thee the heathen for thine inheritance.' The Gloria, Pater Noster, and Ave Maria are to be said, and the whole gone through seven times. Which done let that oil be kept. The time occupied I have tried, and found to be a quarter of an hour."