Part III - Historical Survey of the Porton Down Service Volunteer ...

GB drops on bare skin (mg) No. of volunteers
0.5 5
1 4
2 4
4 4
8 4
10 3
15 8
20 3
25 2
30 1
40 6
Table 8.5. GB doses used in October/November 1951
The degree of ChE inhibition varied considerably between the individuals participating in this
study, which prompted the next human study that sought to understand better the factors
affecting the penetration of liquid GB through skin [67]. The report of the study was published
in 1954 [67] but entries in the experimental records show that the exposures were carried out
in late 1951 and in 1952 [48, 65]. In this study the liquid GB placed on the arms of volunteers
was tagged so that it could be tracked. Some liquid GB was dyed and its activity on the skin
watched under magnification. Other drops were tagged with radioactive phosphorus
(called 32 P) and the activity of the GB was tracked with a Geiger counter. The degree of
radioactivity could be controlled. Thirty five volunteers took part in this study [67].
• Twenty men received a 2 mg drop of GB on each forearm. The drop on one of
the forearms was covered in nylon film to prevent the GB evaporating. The arm
with the uncovered drop was held still inside a fume cupboard.
• Fifteen men had a drop of GB placed on their arm, and in each case the drop
was covered by nylon film. Five men received a 0.6 mg drop; five a 2 mg drop
and five a 3.5 mg drop.
The GB drops were monitored to find out how long it took them to clear the skin either from
penetration or evaporation. Similar investigations were conducted with rabbits. The main
conclusion of the work [67] was that the fat in skin (sometimes referred to as "lipid") played
some part in the penetration of GB and might absorb GB to prevent its penetrating further
through the skin to the blood capillaries beneath.
The study was extended to explore the influence of skin fat on liquid GB penetration. Fat is
present on the skin and below the skin surface. Surface skin fat was removed from clipped
rabbit skin by soaking in acetone, with liquid GB then placed on the skin. A marked
difference in penetration rate was found in rabbits with surface skin fat removed, compared to
the rate in rabbits with skin fat intact. The work was repeated with humans.
• The amount of fat normally present on the forearm skin of man was sampled from
100 men. The mean amount was found to be 81.6 µg/cm 2 .
• Fourteen men took part in a study to compare the rate of penetration of liquid GB
through normal skin and "de-fatted" skin. An area of the left arm was "de-fatted"
by soaking with acetone to remove surface skin fat. The 14 men then had a 2 mg
drop of GB placed on each arm. The activity of the GB on each arm was
monitored to compare the penetration rate through normal skin and de-fatted
skin.
The conclusion from this work was that the amount of surface and sub-surface skin fat affects
the degree of penetration of liquid GB. The less fat that is present, the more deeply through
the skin GB will penetrate and the larger the proportion that would be expected to reach the
72