BACTERIA 



39 



once an hour, the descendants of each individual would in two 

 days number 28 1,500,000,000; and that in three days the prog- 

 eny of a single cell would balance 148,356 hundredweight!'' 

 (Jordan, Genejral^acteriology, p. 61.) Such increase does not 

 take place in nature, however, because of various external in- 

 fluences as well as internal influences produced by the bacteria 

 themselves. The environment is soon changed because of their 

 own physiological activities and multiplication is soon checked. 

 Reproduction is quickly stopped by natural factors like dessi- 

 cation, unsuitable temperature, acid- 

 ity or alkalinity of the medium but 

 many bacteria have the power to 

 resist such adverse conditions by j 

 forming internal spores or Dauers- 

 poren (enduring spores). These are 

 usually spherical, ellipsoidal or oval 

 and possess a dense envelope or 

 spore wall enclosing the majority 



B C ~ ' G 



FIG. 17. Spore formation 

 germination of spores in 

 A, A pair of rods 



and 



bacteria. 



forming spores about 2 o'clock 

 p. M.; B, the same about an 

 of the chromatin granules and some hour later; C, one hour later 

 i /T>* TAN rri still; D, a five-celled rod with 



cytoplasm (Fig. 1 7, D). These spores thre ' e r i pe spores which were 



possess a much higher resistance to placed in a nutrient medium 



after drying for several days; 



external influences than do the cells E, F, the same spores from one 

 from which they are formed (many J g5& 



for example, can withstand a tem- movement. (From de Bary 

 r r o r^ \ a f ter Sedgwick and Wilson.) 



perature of from 70 to 100 C.). 



One spore per cell is the rule, but exceptionally, and in 

 rare instances, two similar spores may be formed. Spore 

 formation in bacteria, therefore, is not a method of reproduction 

 but an adaptation for the preservation of the organism corre- 

 sponding to what is known as the " encysted state "of many 

 unicellular animals. 



Physiology of Bacteria. The food of bacteria is most diverse. 

 The majority are known as saprophytes, that is, they obtain 

 their nourishment from dead organic matter. Many are para- 

 sites, getting their food from other living organisms in the form 

 of complex chemical compounds of proteid substance or proteid 

 derivatives. Some live in the soil and get their food supply and 



