3 6 SPECIES OF GERMS. 



a temperature which would be fatal to others ; some 

 live upon vegetable, some upon animal, matters. 

 Some require solid substance upon and into which 

 they may grow, while others seem to obtain from the 

 atmosphere alone all the materials required for their 

 growth and development. Some enjoy light, while 

 others vegetate freely in darkness. Many of these 

 vegetable germs are almost constantly diffused every- 

 where in the atmosphere, ready to increase a million- 

 fold in a few hours whenever circumstances should be 

 favourable. But all increase and grow in the same 

 manner ; all consist of the growing, living, active, 

 moving bioplasm, or germinal matter, and a certain 

 proportion of the passive, lifeless formed material 

 around it, which has been already referred to. 



It is supposed that germs of different species of 

 vegetable organisms give rise to the phenomena in 

 the system invaded, which are characteristic of the 

 several contagious diseases, and by which they are 

 recognized and distinguished from one another. In 

 the germ stage, however, there are no characters 

 which would enable us to determine the source of 

 the germ ; and whatever differences may exist in the 

 fully developed state, at an early period of existence 

 the embryonic living particles are alike. 



It is not my purpose to direct attention to the 

 various species of microscopic fungi which are known, 

 or to discuss the vexed question concerning species 

 and variety, or to indicate the variety of appearances 



