BLOOD. 223 



consideration the rapidity of the circulation, and the short space 

 of time in which the same blood is supposed to remain in an 

 organ, it is obvious that the detection of the changes in the 

 blood, due to the removal of the secretions, will be a task, if not 

 absolutely impossible, at least extremely difficult. 



The question whether the blood of the same individual pos- 

 sesses any traceable differences, is most intimately connected with 

 the physico-chemical " momentum" of the circulation; although 

 sufficient facts and experiments are still wanting to enable the 

 point to be decisively settled, I believe from an estimate of all 

 that is at present known on the subject, that we are warranted 

 in the assumption that there does exist a difference in the 

 blood of one and the same individual. 



According to Hering's experiments, i (in which he injected 

 ferrocyanide of potassium into the veins of horses,) the blood 

 performs the circuit of the body in from 20 to 30 seconds. 

 Several authorities are opposed to this statement. It is evident 

 that the blood, as it issues from the heart, proceeds in smaller 

 and larger circles ; the smallest are those which it describes 

 through the heart itself and the lungs, the larger are those 

 through the extremities, and it must requii'e different times to 

 go over these different spaces, and besides this, its course is 

 differently impeded in the capillary system of the different or- 

 gans. Thus one portion of the blood may frequently pass 

 through the heart and lungs, while another portion has only 

 made one complete circuit, and traces of the injected ferrocy- 

 anide of potassium which permeates uniformly the whole mass 

 of the blood, may therefore be found after a short time in parts 

 of the system remote from the heart, which have not gone the 

 perfect circuit through the heart, lungs, and all the organs. 

 This appears to be very evident from the fact that some of 

 those salts which are supposed to be rapidly eliminated by the 

 kidneys, may be detected for a considerable period in the blood. 

 Thus I observed,^ that when iodide of potassium was taken at 

 four o'clock in the afternoon, its presence was traceable in the 

 urine till nine the next morning ; and Hering^ found ferrocy- 



• Treviranus Zeitschrift fiir Physiologic, 1832, p. 85. 



= Simon, Die Fraueiimilcti nach ihrera chemischen und physiologischen Verhalten. 

 BerUn, 1838, p. 75. 

 ^ Op. cit. p. 96. 



