MORPHOLOGY AND PHYSIOLOGY OF BACTERIA. 123 



They appear in a typical form in the large bacilli, where, 

 near the centers of the bacilli, highly refracting, shining 

 spots may be seen which are found to stain less rapidly 

 with the "aniline dyes than the rest of the bacilli. They 

 are not to be confused with the unstained spots described 

 as vacuoles. On account of their being formed from a 

 part of the interior of the bacterium, such spores are called 

 endogenous. These spores are found mostly in the bacilli, 

 rarely in spirilla and micrococci. They are what is meant 

 when the word spore is used alone without qualification. 

 The existence of another kind of spore, described as form- 

 ing from the whole of the bacterium (called arthrospore) , 

 is doubtful. At all events, its significance is not at present 

 understood. Spores develop generally, though not always, 

 under adverse conditions of various kinds, as of tempera- 

 ture and of nutrition. They are more resistant to unfavor- 

 able influences of all sorts than are the fully developed 

 bacteria. Spores resist drying, light, heat and chemical 

 agents to a remarkable degree, at times. 



Anthrax spores are said to have been found which could 

 withstand steam for twelve minutes, i-iooo mercuric chlo- 

 ride for nearly three days, or 5 per cent, carbolic acid for 

 more than forty days. The greatest resistance is displayed 

 by the spores of some of the saprophytic bacteria, particu- 

 larly those of hay and potato, which are sometimes not 

 destroyed by several hours of steaming; and bacteria are 

 said to have been obtained from the soil which resisted 

 100 C. for sixteen hours. When cultivated at a tempera- 

 ture as high as 42 C. the anthrax bacillus becomes inca- 

 pable of forming spores. Spores themselves do not mul- 

 tiply, nor do they manifest any activity. Spores may be 

 located at the center of the bacillus, or nearly at one end, 

 when the end of the bacillus is likely to enlarge, making 

 a form having the shape of a drumstick, as takes place 

 ii 



