MORPHOLOGY AND PHYSIOLOGY OF BACTERIA. 119 



string of beads; diplococci, or pairs of micrococci; tetrads, 

 where the individual spheres are grouped in fours; sarcina, 

 where they are grouped in eights making the outline of a cube, 

 resembling a bale or package tied with rope. 



The bacilli are not subdivided in this manner, although 

 their forms vary considerably. The ends are sometimes 

 square, sometimes round. Sometimes they are very short. 



& ^ 



FIG. 32. Bacilli of various forms. 



Sometimes they grow in longer, threadlike forms, in which, 

 however, the transverse markings which indicate the outlines of 

 the individual bacilli can generally be seen, and which re- 

 semble a bamboo rod. Short, oval bacilli may look exceed- 

 ingly like micrococci. Bacilli with rounded extremities, placed 

 end to end, look like strings of sausauges. Under exceptional 

 circumstances, branching forms of the bacilli of diphtheria, 



V 



FIG. 43. Spirilla of various forms. 



tuberculosis, glanders and bubonic plague and various other 

 species have been encountered.* 



The word "bacterium" was formerly used to designate short 

 bacilli which generally formed no spores, while the word "bacil- 

 lus" was restricted to the longer forms in which spore formation 



*See Hill. Journal o) Medical Research. Vol. VII., January, 1902. Loeb. 

 Ibid. Vol. VIII. 1902. 



