14. Transfusion has been practised upon man. At one time, shortly after Harvey's discovery of the "Circulation of the Blood," it became quite a fashionable remedy, it being thought possible by it to cure all forms of disease, and even to make the old young again. But these claims were soon found extravagant, and many unhappy accidents occurred in its practice; so that being forbidden by government and interdicted by the Pope, it rapidly fell into disuse. At the present time, however, it is sometimes resorted to in extreme cases, when there has been a great and rapid loss of blood; and there are upon record several instances where, other means having failed, life has been restored or prolonged by the operation of transfusion. [Sidenote: 15. The seat of the reviving power of the blood? What further is related?] 15. This reviving power of the blood seems to reside in the corpuscles; for transfusion, when attempted to be performed with the serum alone, has, in every case, proved fruitless. Now, though so much depends upon the blood and its corpuscles, it is a mistake to suppose that in them alone is the seat of life, or that they are, in an exclusive manner, alive. All the organs and parts of the body are mutually dependent one upon the other; and the complete usefulness {107} of the blood, or of any other part, flows out of the harmonious action of all the parts. [Sidenote: 16. Changes in the blood? What further is stated?] 16. CHANGE OF COLOR.--The blood undergoes a variety of changes in its journey through the system. As it visits the different organs it both gives out and takes up materials. In one place it is enriched, in another it is impoverished. By reason of these alterations in its composition, the blood also changes its color. In one part of the body it is bright red, or arterial; in another it is dark blue, or venous. In the former case it is pure and fit for the support of the tissues; in the latter, it is impure and charged with effete materials. (The details of the change from dark to bright will be given in the chapter on Respiration.) [Sidenote: 17. Motion of the blood? What is meant by the circulation of the blood? How confined? Discovery made by Harvey?]