Bacteria 33 



be reckoned in numbers." "Fortunately for us," says Woodhead, 

 " they can seldom get food enough to carry on this appaUing rate of 

 development, and a great number die both for want of food and 

 because of the presence of other conditions unfavorable to their 

 existence." 



Sporulation.^ — When the conditions for rapid multiplication by 

 fission are no longer good, many of the organisms guard against 

 extinction by the formation of spores. 



Endospores, or spores developed within the cells, are generally 

 formed in the elongated bacteria — Bacillus and Spirillum — but Zopf 

 has observed similar bodies in micrococci. Escherich also claims 

 to have found undoubted spores in a sarcina. 



Spores may be either round or oval. As a rule, each organism 

 produces a single spore, which is situated either at its center or at its 

 end. When, as sometimes happens, the diameter of the spore is 



/ ■■ , '^ "1 . .■'-'''• , 



V M n' I'" ,,'-. v> . ,; 



Fig. 2. — Spores, showing their various positions in the microorganismal cells 

 (Kolle and Wassermann) . 



greater than that of the bacillus, it causes a peculiar barrel shape 

 bulging of the organism, described as Clostridium. When the dis- 

 tending spore is at the end, a "Trommelschlager," or "drum- 

 stick," is formed. End-spores are almost characteristic of anaerobic 

 bacilli. When the formation of a spore is about to commence, a 

 small bright point appears in the cytoplasm, and increases in size 

 until its diameter is nearly or quite as great as that of the bacterium. 

 A dark, highly refracting capsule is finally formed about it. As soon 

 as the spore arrives at perfection the bacterium seems to die, as if its 

 vitality were exhausted. 



The spores differ from the bacteria in that their capsules prevent 

 evaporation and enable them to withstand drying and the applica- 

 tion of a considerable degree of heat. Very few adult bacteria are 

 able to resist temperatures above 7o°C. Spores are, however, 

 uninjured by such temperatures, and can even successfully resist 

 the temperature of boiling water (ioo°C.) for a short time. The 

 extreme desiccation caused by a protracted exposure to a dry 

 temperature of iSo°C. will invariably destroy them, as will also 

 steam under pressure. Not only can the spores successfully resist 

 3 



