STRUCTURE AND CONSTITUENTS OF BACTERIAL CELL 25 



producing coccus is 0.8 micron in diameter; Micrococcus melitensis, 

 the smallest of the Coccacese, varies in diameter from 0.3 to 0.5 micron. 

 The largest known bacillus, B. biitschlii 1 is 3 to 6 microns in diameter 

 and from 40 to 60 microns in length. The smallest known bacillus, 

 B. influenzse, is but 0.2 by 0.5 micron in diameter; an average sized 

 bacillus would measure about 2 microns in length and 1 micron in 

 diameter. Spirillum colossum 2 is 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 belonging 

 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. 



Weight of Bacterial Cell. The weight of a bacterial cell is depend- 

 ent upon its size and its specific gravity. According to Rubner, 3 the 

 specific gravity of common bacteria varies between 1.038 and 1.065. 4 

 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) 2 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, sixteen hundred million colon bacilli 

 would weight approximately one milligram. For purposes of com- 

 parison 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. Cell Membrane. Ectoplasm. Bacteria appear to possess a 

 special external boundary layer, cell membrane, or ectoplasm, which is 



1 Schaudinn, Arch. f. Protistenk., 1902, i, 306. 



2 Errera, Recueil de 1'Instit. botanique (Universite de Bruxelles), 1901, v, 347. 



3 Arch. f. Hyg., 1903, xlvi, 41; 1890, xi, 385. 



4 Stigell (Cent. f. Bakt., 1908, xlv, 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 1.120 and 1.35, older cultures being as 

 a rule of less specific gravity than younger cultures of the same kind. 



