APPLIED BACTERIOLOGY 



the saccharomycetes, or yeasts. The ' moulds ' consist of 

 slender threads which give rise to the hairy-like patches 

 which are so often seen on various articles of food, such 

 as jam or bread, that have been exposed to warmth 

 and moisture. The ' yeasts ' are ovoid or sausage-shaped 

 bodies which are much larger than the bacteria proper. 



Size of Organisms. — As already stated, the bacteria are so 

 excessively minute that their size baffles description in the 

 ordinary terms of measurement. Most of the bacteria are 

 on the average from gg^oo of an inch long to about five 

 times that length. These measurements do not convey any 

 definite impression to the mind. It is calculated that a 

 thousand million of them could be placed in a hollow tube 

 ■^ of an inch long, or four hundred millions of these 

 organisms could be spread over a square inch in a single 

 layer. The best impression of the size of the bacteria is 

 obtained when it is stated that a gV inch immersion lens 

 gives a magnification of nearly 2,200 diameters ; and that 

 under this power the bacteria appear to be about the size 

 of ordinary print. If we could view the average human 

 being under such circumstances, he would appear to be 

 about four miles in height, or higher than Mont Blanc. 



The standard of measurement employed by bacteriologists 

 is the micro-millimetre ; this is represented by the Greek 

 letter /a. One fi (micro-millimetre) is equal to about ^-5^^ 

 of an English inch. 



The number of cocci in a milligramme of a culture 

 of Staphylococcus pyogenes aureus has been estimated by 

 Bujwid, by counting, at eight thousand millions. Not only 

 do various species differ in dimensions, but considerable 

 differences may be noted in a pure culture of the same 

 species. On the other hand, there are numerous species 

 which so closely resemble each other in size and shape that 

 they cannot be differentiated by microscopic examination 



