22 CLINICAL BACTERIOLOGY. 



temperature-optimum is mostly about 37 C. (98.6 F.). 

 There are microorganisms, however, that live at o C. 

 (32 F.), and exhibit all of their vital manifestations, such 

 as color-formation, light-development, peptonization of 

 gelatin, etc. Forster was the first to obtain such bacteria 

 in pure culture from street-dirt, garden-earth, sea-water, and 

 from the surface of luminous sea-fish. On the other hand, 

 there are found, widely distributed in the earth, the air, the 

 water, the contents of the intestine, etc., bacteria that 

 under aerobic conditions require for their growth tempera- 

 tures of from 50 C. (122 F.) to 75 C. (167 F.) so- 

 called thermophilic bacteria ; under anaerobic conditions, 

 however, these also thrive only between 34 C. (93.2 F.) 

 and 44 C. (111.2 F.). 



The thermal death-point for individual mature bacteria 

 at the upper limit, on short exposure, ranges for the differ- 

 ent varieties between 55 C. (131 F.), 60 C. (140 F.), 

 and 80 C. (176 F.). The death-point at the lower limit 



n o) o o o 



a b c d e f 



Fig. 8. Diagram illustrating speculation : a, Bacillus inclosing a small, oval 

 spore ; b, drumstick-bacillus, with terminal spore ; c, clostridium, with central spore ; 

 d, free spores ; e and/, bacilli escaping from spores (McFarland). 



has been determined only for the smallest number of 

 growths ; many bacteria withstand a temperature of o C. 

 (32 F.) that is, freezing without injury. These state- 

 ments are naturally not applicable to thermophilic and 

 glacial microorganisms. 



In addition to dichotomous division some bacteria, espe- 

 cially the bacilli, and only exceptionally spirilla, and perhaps 

 sarcinae, proliferate through the formation of special perma- 

 nent bodies or spores. (Fig. 8.) In the interior of the cell there 

 forms an ovoid, intensely bright, and refractive body, the 

 spore, which is enveloped in a firm capsule, the spore-mem- 

 brane. One cell generally contains only one spore, which 

 sometimes is situated in the middle, sometimes at an ex- 

 tremity. In the latter event, the rod appears swollen and 

 club-shaped at the corresponding extremity, and it is des- 

 ignated a drumstick-bacterium. (Fig. 8, ^.) If the swelling 

 of the bacillus takes place at the middle in consequence of 



