vi CIKCULATION OF BLOOD : ITS DISCOVEEY 173 



curiosity to discover the circulation in warm-blooded animals, and 

 to grasp it as completely as in the case of the cold-blooded ; 

 hence these vessels " (umbilicals of the chick) " attracted my 

 observation more than any others, and invited my consideration, 

 because they belonged to the said animals. Since the room in 

 which I found myself was insufficiently lighted, and I was 

 determined at all costs to satisfy my curiosity, I decided to 

 examine the egg in the open, under direct sunlight. After fixing 

 it in the apparatus of Lyonet " (a small microscope used by 

 Spallanzani) " I turned the lens upon it, and, notwithstanding the 

 strong light that surrounded me, was enabled by focussing my 

 eyes, to see plainly how the blood iiowed in the entire circuit of 

 the arterial and venous umbilical vessels. Thrilled with this 



FIG. 4s. Holmgren's Apparatus (improvement on Malpighi's method) for observing the pulmonary 

 circulation in a curarised frog. V, screw to regulate position of glass plate, P, which is in- 

 tended to keep the surface of the frog's lung flat ; (.', cannula'jclosed at the end by an elastic 

 membrane, which, when introduced into the glottis and blown up, closes the opening, so that 

 the lung cannot distend. - u j,^ . 



unexpected joy, I felt that I, too, might exclaim, ' I have found it ! 

 I have found it ! ' I made this discovery in May 1771, and employed 

 myself in the summer vacation of that year with its development." 



These observations of Malpighi and of Spallanzani, a century 

 apart, constitute one of the most striking incidents in the history 

 of medicine ; no one has ever contested with Italy the honour of 

 having initiated the direct observation of the circulation. Modern 

 scientists, with more perfect microscopes and a more elaborate 

 technique, have only succeeded in completing the description of 

 the phenomena of the circulation, as visible under the microscope. 

 These must now be briefly described, since they contain some 

 interesting data that should precede the study of haemodynamics. 



VIII. In direct observation of the transparent parts of the 

 living animal under the microscope the blood is seen to circulate 

 in a closed system of capillary canals, which unite the arteries with 

 the veins by a network, and form a continuous circuit. That was 

 the true discovery of Malpighi. 



