112 MANUAL OF BACTERIOLOGY. 



than the rest of the baciUi. 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. They are what is meant when 

 the word spore is used alone without quahfication. The exis- 

 tence of another kind of spore, described as forming 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 temperature and of nutrition. They 

 are more resistant to unfavorable influences of all sorts than are 

 the fully developed bacteria. Spores resist drying, light, heat 



<i«^t 



i I (o % 



^1 



Fig. 44. — Bacteria with Spores. 



and chemical agents to a remarkable degree, at times. Spore 

 formation is not a method of multiplication, since one spore 

 when it germinates reproduces but one cell, and this cell then 

 multiplies. So spore formation seems to be a means of pre- 

 serving the organism under unfavorable environments, and 

 not a process of reproduction in a strict sense. 



Anthrax spores are said to have been found which could 

 withstand steam for twelve minutes, i-iooo mercuric chloride 

 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, particularly those of hay and 

 potato, which are sometimes not destroyed by several hours of 

 steaming; and bacteria which resisted 100° C. for sixteen hours 



