38 Structure and Classification of Micro-organisms 



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 pen- 

 etrated 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 germi- 

 nate, the contents, which have been clear and transparent, 

 become granular, the body increases slightly in size, the 

 capsule becomes less distinct, and in the course of time 

 splits open to allow the escape of a young 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 in- 

 crease in size, develops a characteristic capsule, and presently 

 begins the propagation 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 cocci or micrococci. When they divide, 

 and the resulting organisms remain attached to one another, 

 a diplococcus is produced. Diplococci may consist of two at- 

 tached spheres, though each half commonly shows flattening 

 of the contiguous surfaces. In a few cases, as the gonococcus, 

 the approximated surfaces may be slightly concave, causing 

 the organism to resemble the German biscuit called a "Sem- 

 mel." When a second binary division occurs, and four result- 

 ing individuals remain attached to one another, without dis- 

 turbing the arrangement of the first two, a tetrad, or tetracoc- 

 cus, 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 been 

 given. Migula uses the term micrococcus for the unflagel- 

 lated tetrads, and planococcus for the flagellated forms. 



