Wet ashing using a closed system.

The method is as inexpensive as possible granted that an automatic fraction collector is used. The total capital cost, assuming that one is already performing HAI tests is £50. The technique has been made as simple as possible by removing all strictly unnecessary steps. Accordingly interpretation of results has been based on an appreciation of the overall pattern of HAI activity within the IgM and IgG fractions so that no undue emphasis is placed oneanyone titration. Of course better separation can be achieved by using longer columns of gel but this inevitably increases the cost and technical difficulties. Just as variations in any of the parameters of rubella HAI tests have been shown to alter the results obtained (Schmidt and Lennette, 1970), so do any changes in the method of fractionation of sera. It is emphasized that each of these variables has been investigated and that the detailed procedures described have been selected so that the method remains simple but gives accurate results without difficulties of interpretation. Although the use of the method has been illustrated only for rubella serology, it could be applied to any serological test which will accept an initial serum dilution of 1 in 20 and is not affected by the presence of Nairn PBS plus 0-02% sodium azide.