26 
After extensive discussions and debate, heated most often, the participants 
at the conference agreed that most of the work on the construction of recom- 
binant DNA molecules should proceed, provided that appropriate safeguards, 
principally biological and physical barriers adequate to contain the newly 
created organisms, were used. 
Certain experiments, however, though they were beyond criticism on 
scientific grounds, were believed to pose hazards of such a magnitude that 
they should not be carried out at the present time. Conference participants 
adopted the principle that containment was an integral part of the experi- 
mental strategy, and that the stringency and effectiveness of the contain- 
ment should match the potential risks. It is quite clear that estimating 
the risks is difficult, and in the beginning very likely to be intuitive, 
but there is great hope that our ability to estimate such risks will im- 
prove as we acquire additional knowledge. 
It was accepted as a principle and as a desirable one to set the 
containment requirements high at the beginning, and then to relax them as 
experience permitted. Now, the containment of potentially biohazardous 
agents can be achieved in several ways. The most important one, I believe, 
because it contributes most significantly to limiting the spread of any of 
the organisms carrying recombinant DNAs, is the use of what came to be 
known as biological containment. Biological containment can be achieved if 
(1) the plasmid or viral DNA into which the foreign DNA has been inserted 
is able to propagate only in specified bacterial hosts, and only under de- 
fined conditions and (2) the bacterial hosts are unable to survive outside 
the laboratory environment. 
To me, one of the most refreshing and exciting outcomes of the Asilomar 
exercise was the way the genius of today's molecular geneticists took to the 
task of constructing what one reporter called fail-safe organisms. 
Now, physical containment, exemplified by suitable hoods or special 
rooms which have limited access or negative pressure was recommended as an 
additional factor of safety. In addition, the adherence to good microbio- 
logical practices, which can limit the escape of organisms from the experi- 
mental situation, is essential to the safety of the operation. Consequently, 
the education and training of all personnel involved in these experiments 
is mandatory. We agreed that in practice these different means of con- 
tainment would complement each other, and substantial improvements in the 
ability to restrict the growth of bacterial hosts. 
I would like to make just a few final comments, and that is to empha- 
size something that Dr. Fredrickson pointed out. The concern about the 
potential risks of this type of work was in fact first perceived and raised 
by the scientists, particularly those who were working in the field. Some 
have commented on whether this was a unique social action. I care not to 
comment on that, but I believe that what has followed since reflects the 
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