77 8 POPULAR SCIENCE MONTHLY, 



Robert Boyle (1670), who found, by the use of his air pump, that 

 if he deprived animals of air they died. He vivisected in this 

 way kittens, birds, frogs, fish, snakes, and insects.* Boyle also 

 discovered that by keeping animals in a closed reservoir the air 

 became unfit to sustain life. 



Priestley, a century later (1772), continued Boyle's experiments 

 by keeping mice in air-tight receivers until the air was vitiated 

 and would no longer support life. He then tried to restore the 

 air to its former condition : he rarefied and condensed it, heated 

 it, exposed it to water and earth, and treated it in many other 

 ways, each time testing it with living mice to ascertain whether 

 it would again support life. All this was to no effect. In every 

 case the mice died. Finally, he found that after plants grew for 

 a while in the vitiated air, mice could again live in it. Thus was 

 discovered the important relation between animal and vegetable 

 respiration, and we now plant trees and lay out parks, and call 

 them the " lungs of our cities." Two points must be emphasized 

 here : first, that Priestley could not have done this with dead 

 mice; and, second, that no one except Lawson Tait and Miss 

 Cobbe would have the hardihood to claim that he ought to have 

 used live men instead of live mice, on grounds of moral rights, 

 and from the fact that the physiology of man is " so different " 

 from the physiology of the mouse. 



Turning to still another important line of scientific work, 

 diseases of microbic origin are said to cause four fifths of the 

 sickness in the world. As an example of researches in this field, 

 we may cite the classical work of Edward Jenner. f 



Jenner began to study in earnest the disease cowpox, and its 

 relation to smallpox, in 1775. For twenty-one years he patiently 

 investigated the subject, and found that no one who had once 

 suffered an attack of cowpox was taken with smallpox, although 

 frequently exposed. " Legends of the dairymaids " had told for 

 generations that an attack of cowpox conferred exemption from 

 smallpox forever after. Jenner might have told the same 

 story ; but, if he had not proved the truth of his assertion by 

 experiment, we might still have nothing but " legends of dairy- 

 maids " and no vaccination. 



In May of 1796 Jenner began his experiments. He says 

 (page 29) : " The more accurately to observe the progress of the 

 infection, I selected a healthy boy, about eight years of age, for 

 the purpose of inoculation for the cowpox." This inoculation 

 was followed by an attack of the disease. But Jenner does not 



* Boyle. Philosophical Transactions, vol. v, pp. 2011-2055. 



f Edward Jenner. An Inquiry into the Causes and Effects of the Variolse Vaccinae, 

 December 20, 1799. London, 1801. 



