EDWARD JENNER AND VACCINATION 659 



the capillaries. He says in speaking of circulation in a tadpole's 

 tail, that " Thus it appears that an artery and a vein are one and 

 the same vessel, prolonged and extended." 



A long list of other names might be added to show how gradually 

 our knowledge of the working of the human body has been in- 

 creased. At the present time we are far from knowing all the 

 functions of the various parts of the human engine, as is shown by 

 the number of investigators in physiology at the present time. 

 Present-day problems have much to do with the care of the human 

 mechanism and with its surroundings. The solution of these 

 problems will come from the application of hygiene, preventive 

 medicine, and sanitation. 



Self-Testing Exercise 



' In 1667 Robert Hooke discovered (1) (2) and 



(3) independently found that all (4) and 



(5) are made of cells (6) discovered the circulation of the 



blood (7) first proved that flies developed from eggs. 



PROBLEM n. WHO WERE SOME OF THE CONQUERORS 

 OF DISEASE? 



In the preceding units of this book we have learned something 

 about our bodies and their care. We have found that man is 

 able within limitations to control his environment and make it 

 better. All of the scientific facts that have been of use to man 

 in the control of diseases have been found out by men who have 

 devoted their lives to this work in the hope that their experiments 

 and their sacrifices of time, energy, and sometimes of life itself 

 might make for the betterment of the human race. Such men were 

 Jenner, Lister, Koch, and Pasteur. 



Edward Jenner and vaccination. The civilized world owes much 

 to Edward Jenner, the discoverer of the modern method of vaccina- 

 tion. He was born in Berkeley, a little town of Gloucestershire, 

 England, in 1749. As a boy he showed a strong liking for natural 

 history. He studied medicine and also gave much time to the 

 working out of biological problems. As early as 1775 he began 



