82 Borelli and the Influence [lect. 



"through which they are able to pass while the particles of 

 " another fluid, since their shapes do not match, are excluded." 



And dwelling on the secretion of urine he concludes : 



" Who then would wish to think that the particles of the 

 " blood are picked out, separated from the watery particles (of 

 " the urine) and placed in separate receptacles by some magnetic 

 "virtue or by some ferment, acting like a servant possessing 

 " eyes ? Certainly unless we wish to lay hold of follies and 

 " wonders we are bound to confess that (in the kidneys) there 

 " exist two kinds of orifices after the manner of two sieves, 

 " namely, one a venous one, which by reason of its adjusted 

 " configuration receives the particles of blood only, not those of 

 " the watery urine, and another, the proper vessels of the kidneys, 

 " the shapes of which are fitted for absorbing the particles of 

 " water but not the particles of the blood." 



With the history of the physiology of secretion I propose 

 to deal in a general way presently, and will therefore content 

 myself with thus much of Borelli's views. But I must say one 

 word about his views of the physiology of nerves, though to 

 these also I shall have to return later on. 



The animal spirits of the older writers become in his hands 

 a nervous fluid, a fluid subtle and active but still a fluid subject 

 to the physical laws of fluid, which he calls succus nerveus. 

 He further distinguishes between a succus nerveus nutritivus 

 and a succus nerveus spirituosus. The former governs the 

 nutritive processes of the body, it is through these that nerves 

 exert what we now call a trophic action, the blood supplying 

 material, the nerves the vivifying and plastic force. 



The succus spirituosus is concerned in the production of 

 movements and sensations, it is a fluid subject as we just now 

 said to physical laws. He developes his views as to the 

 mechanical arrangements which determine its flow along the 

 nerves, and in one place compares a nerve to a rod of elder- pith 

 filled with fluid and so through the fluid capable of transmitting 

 oscillations. And throughout he insists that the nervous fluid, 

 the succus nerveus, is essentially a physical fluid. Such a fluid, 

 says he, be it as spiritual, as subtle, and as active as you please 

 is always corporeal and is incapable of acting at a distance. 



