no GENETIC VARIATIONS 



Such changes are particularly striking in the bacteria; here 

 they are of great practical importance, as well as of great 

 interest for the general properties of living matter. The bac- 

 teria are perhaps the lowest organisms for which we can hope 

 to have a knowledge of genetics and variation. They are 

 extremely minute; certain of the common forms are spheres 

 about one micron, or one-thousandth of a millimeter in 

 diameter. Each has the volume of less than one cubic micron. 

 Taking the volume at that figure, calculation shows that it 

 requires fifteen thousand billion of such bacteria to yield the 

 volume of a cubic inch. Thus all parts of the bacterial body 

 are in extremely close relation to the surrounding conditions; 

 all parts are within half a micron, or one fifty-thousandth of 

 an inch, of the enveloping conditions, chemical and physical. 

 There is no part of the bacterial body that is protected from 

 the action of the surroundings by being lodged in the interior 

 of a large body, as is the case in higher organisms. This is a 

 great and important difference. 



We know that the minute bacterial body is the seat of 

 chemical activity of a high potency, manifesting itself as fer- 

 mentations, putrefactions, production of diseases and the like. 

 All this is occurring in closest contact with surrounding con- 

 ditions. Reproduction occurs by division of the body into two. 

 When this division occurs under uniform and favorable con- 

 ditions, usually the two parts produced have the same con- 

 stitution and characteristics as the parent, and this continues 

 indefinitely, so that the stock remains uniform, without 

 genetic variations. If we have side by side two different types 

 of bacteria, when they divide the diversity continues; the 

 characteristics of each type are inherited ; the two types remain 

 constant. For many years there was an effort to show that 

 this is always the case in bacterial reproduction. The uniform 



