FORMS OF BACTERIA 



micrococci always or almost always occur in pairs, and such a com- 

 bination is termed a diplococcus. Some diplococci are united by a 

 thin capsule, which may be made apparent by special methods of 

 staining; in others no limiting or uniting membrane can be seen 

 with the ordinary high powers of the microscope. Again, one fre- 

 quently finds a species which is exactly described by saying that two 

 micrococci are in contact with each other, and move and act as one 

 individual, but otherwise show no alteration ; whilst others are seen 

 which show a flattening of the side of each micrococcus which is in 

 relation to its partner. Perhaps the diplococci in an even greater 



the micro- 



to external i ^ , 



1^ CO »/ 



degree than 

 respond 



>0D 



4» 



<^:t^' 



o 



cocci 



conditions both as regards 

 size and shape. It must 

 further be borne in mind 

 that a dividing micrococcus 

 assumes the exact appear- 

 ance of a diplococcus 

 during the transition stage 

 of the fission. Hence, with 

 the exception of several 

 well - marked species of 

 diplococci, this form is 

 somewhat arbitrary. The 

 third kind of micrococcus is 

 that formed by a number 

 of elements in a twisted 

 chain, named streptococcus 

 (a-TpeTTTOs, twisted). This 

 form is produced by cells 

 dividing in one axis, and 

 remaining in contact with 

 each other. It occurs in a 

 number of difierent species, 

 or what are supposed by many authorities to be different species, 

 owing to their different effects. Morphologically all the streptococci 

 are similar, though a somewhat abortive attempt has been made to 

 divide them into two groups, according as to whether they were long 

 chains or short. As a matter of fact, the length of streptococci 

 depends in some cases upon biological properties, in others upon 

 external treatment or the medium of cultivation which has been used. 

 Sometimes they occur as straight chains of only half a dozen 

 elements ; at other times they may contain thirty or forty elements, 

 and twist in various ways, even forming rosaries. The elements, too, 

 differ not only in size, but in shape, appearing occasionally as oval 



\j~ij\jX'\r\/\j 



Fig. 1. — Diagrams of Various Forms of Bacteria. 



1. Micrococcus. 



2. Diplococcus. 



3. streptococcus. 



4. staphylococcus. 7. Sarciua. 



5. Leuconostoc, show- 8 Bacillus. 



ing Artlrrospores. 9. Spirillum. 



6. Merismopedia. 



