18 BOTANY. 



agents of decay, which is the result of their feeding upon the 

 substance, as, like all plants without chlorophyll, they require 

 organic matter for food. Most of the species are very tenacious 

 of life, and may be completely dried up for a long time with- 

 out dying, and on being placed in water will quickly revive. 

 Being so extremely small, they are readily carried about in 

 the air in their dried-up condition, and thus fall upon exposed 

 bodies, setting up decomposition if the conditions are favor- 

 able. 



A simple experiment to show this may be performed by 

 taking two test tubes and partly filling them with an infusion 

 of almost any organic substance (dried leaves or hay, or a bit 

 of meat will answer). The fluid should now be boiled so as 

 to kill any germs that may be in it ; and while hot, one of the 

 vessels should be securely stopped up with a plug of cotton 

 wool, and the other left open. The cotton prevents access of 

 all solid particles, but allows the air to enter. If proper care 

 has been taken, the infusion in the closed vessel will remain 

 unchanged indefinitely ; but the other will soon become turbid, 

 and a disagreeable odor will be given off. Microscopic exami- 

 nation shows the first to be free from germs 

 of any kind, while the second is swarming> 

 with various forms of bacteria. 



These little organisms have of late years 

 attracted the attention of very many scien- 

 tists, from the fact that to them is due many, -* 

 if not all, contagious diseases. The germs 

 of many such diseases have been isolated, 

 and experiments prove beyond doubt that 

 these are alone the causes of the diseases % 

 in question. 





F B t ^ a drop of water containing bacteria is gx- 



amined, we find them to be excessively small, many 



of them barely visible with the strongest lenses. The larger ones (Fig. 8) 

 recall quite strongly the smaller species of oscillaria, and exhibit similO 



