Day 039 - 20 Oct 94 - Page 73


     
     1        A.  Yes.
     2
     3   Q.   Quantities vastly in excess of anything that a human being
     4        can conceivably get by way of food additives?
     5        A.  Yes, but you will appreciate, Mr. Rampton, that rodents
     6        are small animals with a short lifetime, of a homogeneous
     7        kind, eating a strictly controlled diet.  The human
     8        population whose health we are seeking to protect is
     9        massively larger, massively more diverse and massively more
    10        complicated, and I do not think that one can simply say:
    11         "Oh, because there are no full blown tumours at less than
    12        two per cent in those number of rats to a level of
    13        statistical significance whereby they are assumed not to
    14        have occurred more -- the likelihood of occurring by
    15        accident was less than one chance in 20".  I do not find
    16        that compelling reassurance.
    17
    18   Q.   I do not think you will find, when we come to look at the
    19        conclusion, that is what JECFA thought either,
    20        Dr. Millstone, nor do I think you will find they confined
    21        themselves to rats.  I want to ask you this:  All those
    22        many groups who produced studies using rats did not use the
    23        same groups of rats, did they?
    24        A.  There is some overlap, but there is also some variation
    25        amongst the different kinds of rats that are used.
    26
    27   Q.   Not kinds of rats, the same actual rats?
    28        A.  Certainly not the same rats.
    29
    30   MR. JUSTICE BELL:  Can I ask a question:  If you have group of
    31        rats they are homogenous rats?
    32        A.  They are supposed to be ----.
    33
    34   Q.   As near as you can?
    35        A.  As near as they can.
    36
    37   Q.   That, no doubt, has something to do with the selection of
    38        the size of the group.  If you have heterogeneous animals
    39        or people, as one obviously does, I can see the value of a
    40        survey of a very large number of people because the genetic
    41        differences ----?
    42        A.  May be significant.
    43
    44   Q.   -- may very well be significant, but am I just guessing in
    45        the dark if I say that the fact that animals of your group
    46        are homogeneous, or as near as you can get, will be
    47        something at least of the reason for being content, if
    48        Professor Ito is content, with a group of 50?
    49        A.  No.  I do not think that is correct.  I think you are
    50        coupling together two quite separate considerations. 
    51        Experiments are conducted with laboratory animals in groups 
    52        of varying sizes, some as low as five, some as high as 50 
    53        and so on.  Whatever the group size, there is an attempt
    54        typically to use a homogeneous group of rats.
    55
    56        The reason for doing that is simply in order to factor out
    57        genetic considerations and enable the experimenters to
    58        focus just on the effects of the compound and not the
    59        variations amongst different animals.  There is not a
    60        direct coupling between the homogeneity of the group of

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