26 THE MORPHOLOGY OP BACTERIA 
an inch, in length. Bacteria are the smallest known living organisms 
which have been seen with the microscope. Measured with this unit, 
they exiiibit considerable diii'erences in size. The average-sized pus- 
producing coccus is 0.8 micron in diameter; Micrococcus (Bacillus) 
melitensis, the smallest of the Coccacefe varies in diameter from 0.3 to 
0.5 micron. The largest known bacillus, B. butschlii^ is 3 to 6 microns in 
diameter and from 40 to 60 microns in length. The smallest known 
bacillus, B. influenzae, measures but 0.2 micron in diameter and 0.5 in 
length; an averaged size bacillus would measure about 2 microns in 
length and 1 micron in diameter. Spirillum colossum- varies from 2.5 to 
3.5 microns in diameter. The cholera vibrio is about 2.5 microns long 
and 1 micron in diameter. There are certain living viruses of unknown 
morphology, so-called ultramicroscopic or filtrable viruses, which are 
either somewhat smaller than any known bacteria or more plastic. 
Viruses blonging to this group derive their name from the fact that 
they retain their viability even after passage through the pores of 
standard, unglazed porcelain filters, which will hold back even the 
smallest bacteria.^ Eliava and Suarez* state that the size of the 
bacteriophage is approximately 5 millimicrons. It is possible that 
certain members of the Spirocha^te group may give viable filtrates after 
passage through such filters. 
Weight of Bacterial Cell.— The weight of a bacterial cell is depend- 
ent upon its size and its specific gravity. According to Rubner,^ the 
specific gravity of common bacteria varies between 1 .038 and 1 .065. ^ B. 
coli is an average-sized cylindrical rod (bacillus), measuring 1 micron 
in diameter and 2 microns in length. The volume of a cylinder is the 
product of the diameter squared, multiplied by 0.7854, multiplied by 
the length of the cylinder. The volume of a single colon bacillus 
consequently would be (0.001)^ X 0.7854 X 0.002, or 0.00000000157 
c.mm. The weight of a single colon bacillus would be the volume 
multiplied by the specific gravity, which is approximately 1.040 or 
0.00000000163 mg.; that is to say, 16,000 million colon bacilli would 
weight approximately 1 mg. For purposes of comparison it may be 
stated that a single red blood corpuscle (human) weighs about 0.00008 
mg., about fifty thousand times the weight of a single colon bacillus. 
D. STRUCTURE AND CONSTITUENTS OF THE BACTERIAL CELL. 
The typical bacterial cell consists essentially of protoplasmic cell 
substance, endoplasm, enclosed by a rigid cell membrane, ectoplasm. 
1 Schaudinn: Arch. f. Protistenk., 1902, 1, 306. 
2 Errera: Recueil de I'lnstit. botanique (Universite de Bruxelles), 1901, 5, 347. 
3 Wherry: Jour. Med. Research, 1902, 8, 322. 
^ Compt. rend. Soc. de biol., 1927, 96, 460. 
5 Arch. f. Hyg., 1903, 46, 1; 1890, 11, 365. 
« Stigell (Centralbl. f. Bakteriol., orig., 1908, 45, 487) finds that the specific gravity 
of the same organism varies somewhat with the medium in which it is grown. The 
specific gravity of ordinary bacteria varies commonly between 1.12 and 1.35, older 
cultures being as a rule of less specific gravity than younger cultures of the same kind. 
