THE REVIVAL OF LEARNING 21 



tion, and his knowledge of the laws of physics. His 

 drawings, experiments, and deliberations tell their tale of 

 his unceasing efforts to reach a solution of this abstruse 

 problem. Leonardo ultimately succeeded in grasping 

 quite clearly the nature and action of the valves at the 

 root of the great arteries, and he verified his views by 

 most remarkable experiments. He proved conclusively 

 that the valves allowed the blood to pass in only one 

 direction, and prevented its regurgitation. 



Leonardo, however, gave no complete or clear descrip- 

 tion of the vascular system as a whole. He was not able 

 entirely to emancipate himself from the old idea of the 

 passage of the blood from the right ventricle through the 

 septum into the left ventricle, although he sometimes 

 seems doubtful about the truth of it, for he emphasises the 

 fact that the pores in the septum are invisible. One 

 must remember, however, that Leonardo has not left us 

 any systematic account of the subject ; his remarks are 

 distributed over many years and many manuscripts. 

 Nor is it surprising that Leonardo, who was no physician, 

 should be incomplete and obscure in dealing with one of 

 the most difficult physiological problems. It is also to be 

 remembered that Leonardo did not publish the results 

 of his research it is only comparatively recently that 

 they have been found in his manuscripts. 



But although Leonardo's works remained in manu- 

 script, it must not be assumed that he did not influence 

 his contemporaries and successors. At any rate, soon 

 after his time it is evident that the questions that he 

 had raised concerning the heart and blood-vessels were 

 attracting others, and were generally regarded as an 

 important problem needing solution. This in itself 

 shows that men were beginning to doubt the basis of the 

 current physiological views which were still those of 

 Galen. Thus Jacob Berengar of Carpi, who died twelve 



