98 Malpighi and the Physiology [lbct. 



" You will place on a transparent plate the lung, illuminated from 

 " below by the light of a lamp conducted through a tube and 

 " you will bring to bear upon, it a microscope of two lenses. In 

 " this way the vessels distributed in a ring-like fashion will be 

 " disclosed to you. By the same arrangement of the instrument 

 " and the light you will observe the movement of the blood in 

 " the vessels lying in the field of view. And you will yourself 

 " be able, with different degrees of light which escape description 

 " by the pen, to devise other things. Concerning the movement 

 "of the blood, however, one thing presents itself as worthy 

 " of your speculation. The auricle and heart being ligatured 

 " and so all movement and impulse which might be conveyed from 

 "the heart to vessels still connected with it being removed, 

 "the blood still flows towards the heart along the veins and 

 " distends these by its movement and copious supply ; and 

 "this lasts for several hours. At the end however, especially 

 "if it be exposed to the sun's rays, it is not the subject of 

 " the same continued movement but as it were of alternating 

 "impulses; the blood, moving to and fro, progresses and then 

 " recedes along the same way. And this takes place also even 

 " when the heart and auricle have been removed from the body. 



" Turning therefore to the former problems demanding 

 " solution, it may, by analogy, and from the simplicity which 

 " Nature uses in all her works, be concluded from these results 

 " that that network which I once thought to be nervous in nature 

 " is really a vessel attached to the vesicles and sinuses carrying 

 " thither the mass of the blood or carrying the same away, and 

 " that although in the lungs of the more perfect animals a vessel 

 " seems sometimes to leave off and to gape in the middle of the 

 " network of rings, yet it is probable that, as in the cells of the 

 " frog and the tortoise, the vessel in question is prolonged further 

 " into very small vessels after the form of a network, although 

 " these on account of their exquisite fineness escape our senses." 



This was the first observation of the capillaries. A few 

 years later, in 1668, that patient and accurate Dutch observer 

 Anton van Leeuwenhoek observed them in fishes and in 

 amphibia, and gave a fuller description of them. With the clue 

 thus given their presence was shewn or taken for granted in all 



