22 



THE BLOOD 



the minutest variations of the blood-pressure, the 

 multiple influences of the nervous system on the 

 heart and blood-vessels, the relations between 

 blood-pressure and secretion, the automatism of 

 the heart-beat, the influence of gravitation, and 

 other finer and more complex issues of physiology. 

 But, even if one stops at Marey's book, now forty 

 years old, there is an abundant record of good 

 work, from the discovery of the circulation to the 

 invention of the sphygmograph. 



