,126 FRAGMENTS OF SCIENCE. 



sufficiently large to cause the resulting disease to assume 

 an epidemic form. 



" I may remark further that the infection of the air in 

 these two cases was obviously not the work of chance, but 

 only represented the effect of agencies which are always in 

 operation where this fever prevails. 



" The phenomenon is, in fact, merely the expression of a 

 general law. 



" The germs cast off in the liquid excreta of contagious 

 diseases rise into the air by no power of their own, but in 

 virtue of the very same physical conditions which cause the 

 germs of the great tribe of Infusoria, which, as their name 

 bespeaks, breed in liquids, to rise in swarms into the same 

 medium. 



" If there were time or need, I could show, by evidence 

 quite as decisive, that all these statements apply equally to 

 cholera also. 



" I do not know that there is any thing in these data to 

 suggest additional matter for your essay, but I have thought 

 it worth while to bring them under your notice, harmoniz- 

 ing as they do with your own investigations which show 

 by such striking phenomena that air and water are equally 

 objects of distrust. 



" As to the germ-theory itself, that is a matter on which 

 I have long since made up my mind. From the day when 

 I first began to think upon these subjects, I have never had 

 a doubt that the specific cause of contagious fevers must be 

 living organisms. 



" It is impossible, in fact, to make any statement bearing 

 upon the essence or distinctive characters of these fevers, 

 without using terms which are of all others the most distinc- 

 tive of life. Take up the writings of the most violent oppo- 

 nent of the germ-theory, and, ten to one, you will find them 

 full of such terms as ' propagation,' ' self-propagation,' ' re- 

 production,' 'self-multiplication,' and so on. Try as he 



