666 



PRINCIPLES OF GENERAL PHYSIOLO(;V 



through interspaces in the tissues. A kind of pump, the heart, is very early met 

 with, even in such simple vascular systems, and it serves to accelerate the flow. 

 In some organs in the higher vertebrates there are remains of this lacunar system 

 of circulation, in the spleen, for example. 



History. It is a matter of common knowledge that Harvey (1616 and 1628) 



FIG. 220. PORTRAIT 



LEEUWENHOEK. 



(From the reproduction in Jl. R. Micron. Soc., 1913, part 2. 

 By the kindness of the Council. ) 



was the first to grasp the fact that the function of the heart is to drive the blood 

 along the blood vessels and back to the heart in a circle. This knowledge he 

 gained by experiments on living animals, combined with deductions from the 

 direction in which the valves of the heart and of the veins allowed the blood 

 to flow. The first statement appears to be in the manuscript notes of lectures 

 given in 1615 to the College of Physicians of London. These notes have been 

 published in facsimile by the College of Physicians, at the instance of the late 

 Sir Edward Sieveking. The reader may be interested to glance at Fig. 218, in 

 which a page from this facsimile is reproduced. The statements to which Harvey 

 affixes his initials, he intends 4o claim as his discoveries. The transcription of 



