34 Structure and Classification of Micro-organisms 



a considerable degree of heat, but they are also unaffected by cold 

 of almost any intensity. Von Szekely* found anthrax spores ca- 

 pable of germination after eighteen years and six months in some 

 dried-up old gelatin cultures found in his laboratory. 



Arthrospores.— The formation of arthrospores is less clear, and 

 seems to be the conversion of the entire organism into a spore or 

 permanent form. Arthrospores have been observed particularly 

 among the micrococci, where certain individuals become enlarged 

 beyond the normal, and surrounded by a capsule. 



Though the cell-wall of the adult bacterium is easily penetrated 

 by solutions of the anilin dyes, it is difficult to stain spores, which are 

 distinctly more resistant to the action of chemic agents than the 

 bacteria themselves. 



Germination of Spores. — When a spore is about to germinate, the 

 contents, which have been clear and transparent, become granular, 

 the body increases sUghtly in size, the capsule becomes less distinct, 

 and in the course of time spUts open to allow the escape of a young 



c 

 a b [\ d e i. 



C^^ <rz — o) a O o cs=> Q=> 



Fig. 3. — -Diagram illustrating sporulation: a, Bacillus inclosing a small oval 

 spore; b, drumstick bacillus, with the spore at the end; c, clostridum; d, free 

 spores; e and /, bacilli escaping from spores. 



organism. The direction in which the capsule ruptures varies in 

 different species. Bacillus subtilis escapes from the side of the 

 spore; Bacillus anthracis from the end. This difference can be 

 made use of as an aid in differentiating otherwise similar organisms. 



So soon as the young bacillus escapes it begins to increase in size, 

 develops a characteristic capsule, and presently begins the propaga- 

 tion of its species by fission. 



Morphology .^ — The three principal forms of bacteria are spheres 

 (cocci), rods (bacilli), and screws (spirilla). 



Cocci. — The spheric bacteria, from a fancied resemblance to 

 little berries, are called Coccus or Micrococcus. When they divide, 

 and the resulting organisms remain attached to one another, a 

 Diplococcus is produced. Diplococci may consist of two attached 

 spheres, though each half commonly shows flattening of the con- 

 tiguous surfaces. In a few cases, as the gonococcus, the approxi- 

 mated surfaces may be slightly concave, causing the organism to 

 resemble the German biscuit called a "Semmel." When a second 

 binary division occurs, and four resulting individuals remain at- 

 tached to one another, without disturbing the arrangement of the 

 first two, a tetrad, or Tetracoccus, is formed. To the entire groups 

 of cocci dividing in two directions of space so as to produce fours, 

 eights, twelves, etc., on the same plane, the name Merismopedia has 

 * "Zeitschr. fiir Hygiene," 1903, xliv, 3. 



