X. Discovery that the veins of the bat's wing (which are furnished with valves) are endowed with rythmical contractility, and that the onward flow of blood is accelerated by each contraction

In entering on the investigation of the state of the blood and the blood-vessels in inflammation excited in the web of the Bat’s wing, I applied myself, in the first place, to the study of the distribution, structure and endowments of the arteries, capillaries and veins of the part, and of the phenomena of the circulation in them. I had not observed the circulation under the microscope long, before I was struck with something peculiar in the flow of blood in the veins; I therefore directed my attention to them, and discovered that they contracted and dilated rythmically. Following the veins for some extent in their course, I further discovered them to be provided with valves, some of which completely opposed regurgitation of blood, others only partially.