BIRTH OF EXPERIMENTAL PHYSIOLOGY 47 



both in botany and zoology. His numerous memoirs 

 were published in a collected form in the volumes so 

 well known to all students of botany as the Statical 

 Essays, the first deaUng with problems in plant physiology, 

 the second with corresponding problems in animal 

 physiology. The Vegetable Staticks, with which we are 

 mainly concerned, is dated 1727, and in it we find evidence 

 that entirely supports the title often given to its author of 

 being the founder of the experimental physiology of plants. 

 You will remember the quaint ideas that Grew had 

 on plant nutrition, the part played by various filtrations, 

 fermentations, and what not. There is nothing of this 

 vague theorising in Hales's book. The greater part of it 

 is a record of a consecutive series of experiments, with 

 a minimum of space devoted to deductions and general 

 conclusions. Early in his career Hales had made experi- 

 ments on arterial blood-pressure in animals, some of 

 which would greatly shock the present-day anti-vivi- 

 sectionist, and he expresses the wish that he " could 

 have made the hke experiments to discover the force 

 of the sap in vegetables.'' An attempt to stop bleeding 

 in a badly pruned vine, by means of a piece of bladder 

 tied over the wound, gave him the idea of the manometer— 

 " by mere accident I hit upon it," he says. Once again 

 you will notice the research starts with an attempt to 

 compare the functions of the animal and the plant ; the 

 arterial pressure in the one is to find its counterpart in 

 the root pressure of the other. Having satisfactorily 

 demonstrated this pressure he is naturally led to enquire 

 as to its cause. He found that the pressure showed a 

 daily periodicity, and that it was affected by changes in 

 temperature. Since the pressure was upward only by 

 way of the wood he saw that the term " circulation," 

 in the sense in which it had been used by Harvey, was 

 not apphcable to the sap movements, and hence he 

 denied the existence in plants of anything comparable 

 with the arterial and venous flow in the animal. He 



