186 THE BLOOD. 



diately after their expulsion, the observer is inclined to attri- 

 bute their escape from the clot to these movements ; this notion 

 is, however, proved to be erroneous by what follows. In a 

 short time (usually about forty-five minutes after the com- 

 mencement of the observation), the colored corpuscles begin 

 to participate in the process, and escape from the still sharply- 

 defined edge of the clot in such numbers that the liquid becomes 

 so crowded with them, that microscopical examination is no 

 longer possible. If now the tube is removed from the stage 

 and placed vertical!}', it is seen, after a time, that the corpuscles 

 subside to the bottom of the tube, leaving a clear space con- 

 taining serum above. Here, then, we have a process which we 

 might at first sight be disposed to regard as a resolution of the 

 coagultim ; the appearance is, however, deceptive, for if the 

 tube is discharged into a watch-glass and examined under a 

 low power, the coagulum is easil}- found as a thin cord of fibrin 

 floating in the liquid. In short, the whole process of emigra- 

 tion of the corpuscles and liquefaction of the clot is the conse- 

 quence of the contraction of a reticulum of fibrin of such extreme 

 looseness, that it is incapable of retaining the corpuscles in its 

 meshes. 



9. The two experiments last related prove, as regards the 

 blood of the frog, that, under certain conditions, coagulation 

 occurs very imperfectly, even though the blood be removed 

 from the body, and consequently that Briicke's inference, that 

 the circulating blood is prevented from coagulating by the in- 

 fluence of the living vessel, need no longer be maintained. The 

 following experiment, devised b}^ Mr. Schafer, which has been 

 repeated a great number of times in the laboratory of Univer- 

 sity College, proves this much more conclusively and satisfac- 

 torily. A glass tube, three or four inches long, is drawn out 

 at one end into an arterial canula of the usual form and of 

 suitable size. A frog having been secured in the usual way 

 (see 46) in the prone position, the heart is exposed and the 

 right aorta ligatured. A clip is then placed on the left aorta 

 at its origin from the bulb.. The canula (Fig. 193, a) is then 

 inserted and secured in the left aorta, and the tuba supported 

 vertically by a suitable holder. This done, and the clip having 

 been removed, the blood is allowed to flow into the tube. It 

 rises to a height which varies according to the vigor of the 

 animal and the quantity of blood which its vascular system 

 contains, the blood column oscillating with the contractions of 

 the heart. If now the tube is left to itself, no coagulation takes 

 place. In a very few minutes the corpuscles begin to subside, 

 leaving an upper layer of clear liquid, the depth of which gradu- 

 ally increases. If it is removed with a capillary pipette and 

 submitted to examination, it is found to possess all the proper- 



