8 APPLIED BACTERIOLOGY 



name Leptothrix. Other kinds branch, and are known by 

 the name of Cladothrix. 



All these various shaped organisms are loosely spoken of 

 as bacteria. In addition to these forms are two other 

 classes of micro-organisms, namely, the moulds and 

 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 -^twu-u oi 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 millions of them could be placed in a hollow tube 

 ■2V 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 ^V 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 fi. One //. (micro-millimetre) is equal to about 2TW!r 

 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 



