SIZE AND STRUCTURE OF THE BACTERIAL CELL. 25 



diameter of a blood cell. The average micrococcus has a 

 diameter of about 1 /;-, or sdnnr of an inch. 



The width of the average bacillus is about 1 ;j.. The 

 length will vary usually from 2 to 4 //. The thickest bacilli, 

 like the B. crassus, are said to have a width of 4 p.. Usually 

 several bacilli must be placed end to end to correspond to 

 the diameter of the red blood corpuscle. 



From the dimensions given it is evident that an enor- 

 mous number of bacteria may be present in a relatively 

 small volume. One milligram of the pure cells of the 

 golden pus-producing micrococcus will contain about 

 2,000,000,000 individuals. One grain of this material would 

 therefore contain 128,000,000,000 cells. 



In view of the extremely minute size of bacteria it is 

 evident that they are very close to the limit of micros- 

 copic vision. It is manifestly impossible to make out much 

 of any structure in such small organisms. The ordinary 

 plant or animal cell can be readily shown to consist of 

 a cell-wall, a protoplasm and a nucleus. It may there- 

 fore be expected that the bacterial cell will likewise 

 consist of a cell-wall, containing the protoplasm and the 

 nucleus. 



It has been supposed in the past that the bacterial cell 

 possessed a cell-wall which did not stain readily and which 

 was composed of cellulose or woody fibre. There can be 

 no question regarding the existence of an outer membrane 

 or envelope, but its chemical composition is undetermined. 

 Certain sarcines and a few bacilli have been said to give 

 cellulose reactions, but these observations have not been 

 confirmed by subsequent investigators. Some of the reac- 

 tions employed in the detection of cellulose cannot be 

 considered as characteristic. Thus, the production of a 

 reducing substance on treatment with an acid may be due 

 to cellulose, but it may also be due to the presence of a 

 glyco-proteid. 



