164 CLASSIFICATION OF THE MICRO-ORGANISMS. 



and incompletely destroyed by the most various chemical 

 agents. It is clear that on account of these properties 

 the spores possess a special hygienic interest; for 

 example, the possibility of exterminating a pathogenic 

 fungus from the surroundings of man by disinfecting 

 means depends chiefly on whether or not the fungus 

 in question forms resistant resting spores. All resting 

 spores do not show the same high degree of resisting 

 power; different spores have apparently very different 

 powers of resistance, but a certain increased power of 

 resistance, notably the capability of retaining their 

 vitality for a long time in a dry state, must be held to 

 be a necessary characteristic of spores. Bearing this in 

 mind, we require better reasons than have as yet been 

 brought forward for assuming the existence of the 

 so-called arthrospores. The micrococci and most of 

 the spirilla are probably characterised by complete 

 absence of resisting spores ; at any rate if we examine 

 strongly heated mixtures of bacteria to see what forms 

 have retained their vitality after exposure to a tempera- 

 ture of 80 100 C., we find only the bacilli which form 

 resting spores, and none of the other vegetative forms. 



3. Characteristics of the Cultivations of the Fission 

 Fungi. 



When in considerable masses, whether these consist 

 i8tics C of r the simply of apposed organisms and swarm formation, or 

 cultivations of O f zooglaea, the bacteria become visible even to the naked 

 the fiss-.on .1 ,-, -,i T^V -, -, 



fungi. eye. In fluids they cause either diffuse or cloudy mud- 



diness, or they cover the surface in the form of thin or 

 thick scums ; or the zooglaea masses form swimming 

 flakes; or a powdery deposit of bacteria forms at the 

 bottom, especially when the nutritive materials in the 

 fluid are exhausted and are no longer able to supply 

 food for a further multiplication of the organisms. 

 Some species of bacteria can also undergo extensive 

 multiplication in fluids or on solids without anything 

 becoming noticeable to the naked eye. The appear- 

 ance of the colonies of bacteria on solid substrata, 



