ISOLATION OF ANAEROBES 455 



VII. Separation of organisms before sowing was suggested by 

 Stoddard, who shook his material with sea sand to separate en- 

 capsulated or autoagglutinated organisms. Dr. K. F. IMeyer 

 tells me that he has found such technique useful in isolating an- 

 aerobes from soil and from old meat cultures which had sporu- 

 lated heavily. Such separation is not necessary when fresh 

 cultures are used. 



VIII. Isolationhy various colony methods. Because of the confu- 

 sion that exists as to the purity of cultures of anaerobes, it will 

 be well to study the biological factors involved in the genesis of 

 bacterial colonies. A colony is an aggregation of organisms that 

 are prevented from mixing with other organisms by a physical 

 obstruction. A colony may be defined as follows: 



a. From one single organism — the ideal colony for isolation 

 purposes. 



b. From two or more organisms descended directly or indirectly 

 from one organism — a satisfactory colony for isolation purposes. 



c. From two or more organisms of closely related strains — the 

 most undesirable type of colony for isolation purposes. 



d. Or from two or more organisms of unrelated strains — an un- 

 desirable type of colony for isolation purposes. This type or a 

 contaminated pure colony is sometimes useful in procuring a new 

 proportional mixture of strains. 



Broadly speaking a colony may consist of any number of 

 organisms from one to infinity. Technically speaking a colony 

 consists of the organisms confined within a certain radius 

 inside of or on the surface of the mass of colloid gel. For 

 purposes of discussion, let us define a bacterial colony 

 as the uncontaminated descendants of a very small number 

 of organisms, irrespective of the medium in which they are 

 found. It will be. realized that this definition covers perfectly 

 the biological factors involved in the derivation of any ordinary 

 agar or gelatin colony. 



Colony methods available for the isolation of anaerobes are the 

 following: 



