An instrument which I had made several years ago presents some advantages and may therefore be of use to others who have to deal with serum-diagnosis, etc. The chief advantage of the instrument is that after each dilution has been made it is ready for making further dilutions without cleansing it. The instrument is moreover easy to manipulate. It may be described as essentially a “reversed Thoma-Zeiss pipette”, the graduations being marked upon the upper section of the tube, instead of on the lower section. The accompanying figure makes the construction of the instrument clear.