THE LIFE HISTORY OF BACTERIA. 51 



organism is growing' under tlie best possible, conditions it 

 will not give rise to spores. If, for instance, it is trans- 

 planted every few hours in order to avoid the formation of 

 waste products it can be maintained indefinitely in the 

 vegetating condition. It is for this reason that bacteria 

 growing in the blood of a living animal do not form spores. 



The temperature is an important factor in spore pro- 

 duction. The formation of spores has not been observed 

 to occur below 16°.' The optimum temperature is at 30 — 35°. 

 Certain bacteria will not form spores in the absence of oxy- 

 '' gen, whereas other bacteria require very little or no oxygen. 



The composition of the soil has much to do with sporu- 

 lation. The presence of calcium salts and the absence of 

 pepton favor spore production. On the other hand, the 

 presence of minute amounts of carbolic acid, or of mercuric 

 chloride will so alter an organism as to give rise to a spore- 

 less variety. Asporogenic bacteria may also result from 

 prolonged artificial cultivation on the ordinary laboratory 

 media. The anthrax bacillus which has been cultivated for 

 some years never gives rise to spores when grown on the ordi- 

 nary media. The failure in spore production in such instan- 

 ces is similar to the loss of motion of certain bacteria under 

 like conditions (p. 88). The asporogenic varieties may be 

 compared to the highly cultivated, seedless flowering plants. 



In its earliest stage, the spore appears within the cell 

 as a bright, oil-like, refracting body. This appearance 

 becomes well marked when the spore is fully developed, 

 that is to say, when the spore-mass "has surrounded itself 

 with its characteristic spore-wall. It is especially marked 

 in the free spore. The spore,, as a rule, possesses the same 

 width as the parent cell. It is a short oval or roundish 

 body and can, as a rule, be readily recognized by its micro- 

 scopical appearance and by its behavior to stains. 



1 Unless otherwise indicated the temperatures given in this 

 work are Centigrade. 



