37 
containment. Later today Dr. Barkley will describe some of the details for 
you, and also show a movie which describes the strictest available facili- 
ties. 
For now, it will be sufficient for me to tell you that the guidelines 
specify four levels of physical containment. They are termed PI, P2, P3 
and P4 in the document, in the order of increasing levels of containment. 
PI, the lowest level, consists of the use of the standard microbiologi- 
cal practices that I mentioned before. The P2 and the next higher level, 
P3, each require special procedures and facilities designed to limit to in- 
creasing extents any possible accidental escape of potentially hazardous 
organisms . 
Finally, P4, the maximum level of containment requires sophisticated 
and isolated facilities designed for maximum containment. Each of the 
levels P2 through P4 assumes that the techniques demanded by PI, the stan- 
dard microbiological practices, will be followed; and furthermore, for each 
level, the training of personnel in the relevant procedures is mandatory. 
Training is to include both the technical manipulation and instruction in 
the biology of the relevant organisms and systems. 
The third approach to the problem of containing potentially hazardous 
organisms within the laboratory is termed biological containment. Biologi- 
cal containment is defined as the use of host cells and vectors with limited 
ability to survive outside the very special and fastidious conditions which 
can be maintained in the laboratory, but are unlikely to be encountered by 
escaped organisms in natural environments. Biological containment is an in- 
tegral part of the experimental design, since the host and vector will need 
to be chosen in any given experiment with a view both to the purpose of the 
experiment and to containment. It is important to stress, as the guidelines 
do, that physical and biological containment procedures are complementary 
to one another, each one serving to control possible failures in the other. 
The use of both in a given experiment affords much higher levels of contain- 
ment than either one alone; therefore, as you will see, the guidelines 
always recommend both a particular level of physical containment and a level 
of biological containment for any given experiment. 
It is also of some importance that the guidelines recommend that publi- 
cations describing work on recombinant DNA include a description of the 
containment procedures that have been used. 
The first class of experiments described in the guidelines are those 
which are not to be carried out at the present time. While it may be argued 
that a combination of P4 physical containment and a high level of biological 
containment could essentially contain these recombinants, the magnitude of 
the possible dangers, were containment to fail, dictates that these experi- 
ments be deferred. The class of experiments is summarized on the next slide. 
[178] 
