Microbial Structures and Staining Reactions 87 



tions, however, have led the way by expressing weights and mea- 

 sures in that metric language understandable to fellow scientists 

 throughout the world. 



Since this is the first contact some students will have with the 

 formal field of science, they would do well to gain a mental picture 

 of the metric equivalents of some of our weights and measures. A 

 review for other individuals might be profitable. A cubic centi- 

 meter (cc), also commonly referred to as a milliliter (ml), should 

 come to mean about twenty small drops, just as a liter (1000 ml) 

 should be visualized as a volume slightly greater than a quart. An 

 object described as being ten millimeters (mm) long should be 

 thought of as about two-fifths of an inch in length. Beginners in 

 science are cautioned not to confuse millimeters (mm) with 

 milliliters (ml). The former is a linear measurement (length), 

 while the latter term refers to a volumetric deteraiination. 



It is unnecessary to outline the complete metric svstem in a book 

 of this type, but the mention of a few of the more commonly em- 

 ployed terms seems justified. 



Length: One United States yard is ''' ^' *^ % 9 ;{ 7 meter. Or to express 

 this in another way, 1 meter equals 39.37 inches. 



1 meter =10 decimeters 



1 decimeter =10 centimeters 



1 centimeter = 10 millimeters 



1 millimeter = 1000 microns 



1 micron = approximately 1/25,000 of an inch. 



In measuring light waves we employ the Angstrom unit, which 

 is 1/10,000 of a micron, or 1/10,000,000 of a millimeter. Ordinary 

 light-type microscopes cannot distinguish objects smaller than 



