474 EEPORT OP THE SBORETARY OF THE :'' 



It may seem that undue importance is attached to this 

 microscopic examination for fungus growth, but the lines of 

 investigation in physical science, into the nature and origin of 

 contagious and epidemic diseases, all converge towards this 

 germ theory of disease. In a recent lecture on " Haze and 

 Dust," Prof. Tyndall says : " Side by side with these researches 

 and discoveries, and fortified by them and others, has risen the 

 germ theory of epidemic disease. The notion was expressed 

 by Kircher, and favored by Linna3us, that epidemic diseases 

 are due to germs which float in the atmosphere, enter the body, 

 and produce disturbance, by the development, within the body, 

 of parasitic life. The streogth of this theory consists in the 

 perfect parallelism of the phenomena of contagious disease 

 with those of life. As a planted acorn gives birth to an oak, 

 competent to produce a whole crop of acorns, each gifted with 

 the power of reproducing its parent tree, and as thus from a 

 single seed[ing a whole forest may spring ; so these epidemic 

 diseases literally plant their seeds, grow, and shake abroad new 

 germs, which, meeting in the human body their proper food 

 and temperature, finally take possession of whole populations. 

 Thus Asiatic cholera, begining in a small way in the delta of 

 the Ganges, contrived, in 17 years, to spread itself over nearly 

 the habitable globe. The development from an infinitesimal 

 speck of the virus of the small-pox, of pustules, each charged 

 with the original poison, is another illustration.*' 



By similar reasoning, persons have been led to suspect the 

 foreign origin of many diseases in vegetables, especially if the 

 disease exhibits contagious properties; but, unlike the 

 researches in animal disease, the vegetable physiologist has been 

 able, in some instances, to find the fungus origin of disease, and 

 hence to strongly suspect it even when it cannot be found. 

 The writer in the Gardener's Monthly, from which I have 

 already quoted, in discussing the probable fungus origin of 

 the Yellows, says : "And now, in regard to the Yellows in the 

 peach tree, we are almost prepared to abandon all we have said 



