38 LEISURE-TIME STUDIES. 



And if, as I trust I have shown you, these great results of 

 saving and prolonging life have sprung from, and been per- 

 fected by zoological observation, you will not require much 

 further illustration of my second proposition, that zoology 

 has something to do with the health and well-being of 

 communities. 



But every time you see a child vaccinated, you are also- 

 beholding a tacit recognition of the " germ theory," and of 

 the value of biological study and research. The vaccine 

 lymph contains the particles or germs of the mild fever 

 which has so valuable a protective influence on the child. 

 And you are thus simply and intentionally, and with good 

 result, exposing the human organism to the attack of the 

 lower organisms which in more virulent form cause the 

 dreaded small-pox epidemic. In following up the proposal 

 to "stamp out" infectious disorders, we are simply treading 

 in the footsteps of Redi and his successors ; and if in the 

 future we are privileged to reach this higher perfection of 

 the physician's art, and to see epidemic disorders finally 

 trodden underfoot, we shall have to thank the labours of 

 biologists and physiologists for thus saving the people from 

 perishing by the fulness and worth of their knowledge. 



If also you will read the account and I know of no 

 subject more attractive to the ordinary reader, as well as to 

 the student of zoology of Pasteur's researches into the 

 nature and cause of the great silkworm-disease, known as 

 Pebrine, which decimates that insect-species, as cholera 

 slays its human thousands, you will discover how a 

 zoological study saved the commercial prosperity of France. 

 Prior to Pasteur's researches, the silkworms died in multi- 

 tudes from the mysterious epidemic, and blank ruin stared 

 the silk-growers and cultivators in the face. When, how- 

 ever, by careful study of the causes and conditions of the 

 disease, Pasteur had made himself master of the situation, 

 and had found that a minute plant-organism, propagating 

 itself within the bodies of the silkworms and readily con- 

 veyed from one to the other, was the cause of the disorder, 



