INTRODUCTORY i,8-9 



1943-5 H. J. Conn, Victor Burke, Barnett Cohen, C. H. Werkman, M. W. 

 Jennison, J. A. Kennedy, L. S. McClung, A. J. Riker. 



1946-7 H. J. Conn, G. H. Chapman, Barnett Cohen, I. C. Gunsalus, M. W. 

 Jennison, L. S. McClung, A. J. Riker, C. E. ZoBell. 



1948- M. W. Jennison, G. H. Chapman, Barnett Cohen, H. J. Conn, I. C. Gunsalus, 

 J. A. Kennedy, L. S. IVFcClung, A. J. Riker, C. E. ZoBell. 



USE OF THE MANUAL 



Pitfalls to be Avoided by the Student 



In studying bacterial cultures with the object of identifying them 

 or describing them, the student is apt to run onto certain pitfalls. 

 Many of these are well known and others less fully appreciated. At 

 the risk of making comments that are already too well known by stu- 

 dents of bacteriology, a few words concerning some of these pitfalls 

 do seem called for here. They arise primarily from three sources: 

 first, the danger of impure cultures; second, confusing results due 

 to variation of bacterial species; third, differences in methods of 

 study. 



The danger in impure cultures is, of course, thoroughly understood. 

 Unfortunately, however, the second consideration just mentioned 

 makes it more important to emphasize the danger of impure cultures 

 today than was the case 25-30 years ago. In those days bacteriolo- 

 gists quite generally accepted the idea of monomorphism; and when- 

 ever a culture was observed to be noticeably abnormal either in 

 morphology or physiology, it was promptly discarded as a contami- 

 nant. When, however, it began to be learned that even the most 

 strictly guarded pure cultures might show changes in morphology 

 during their life history, and then later when it was realized that the 

 same organism might occur in two or more phases showing distinctly 

 different cultural and physiological characteristics, the old ideas of 

 monomorphism were decidedly upset. As a result of the changing 

 point of view, it is very easy for a careless student today to believe 

 that he is observing two phases of the same pure culture when actually 

 one of his "phases" is a contaminant. This makes constant checking 

 as to purity of cultures even more important than it was before dis- 

 sociation into phase variants was generally accepted by bacteriolo- 

 gists. 



Accepting the idea of dissociation presents other diflSculties to the 

 student. Without exhaustive study, it is sometimes very easy to 

 describe two phases of the same species as though they were different 

 organisms. It is also easy to prepare a description of some culture 

 which is an illogical jumble of the characteristics of two or more 



