Observations on the Blood of Certain Ascidians , with Special Reference to the Biochemistry of Vanadium

AMONG the numerous idiosyncrasies, both anatomical and biochemical, which distinguish the Tunicata so sharply from all other animals, few are more striking than the two features of their blood which were first revealed by Henze (1911)— the presence in it of an organic compound of vanadium, and also of very considerable quantities of free sulphuric acid. In spite of the publication, since that date, of numerous histological and a few chemical studies on the subject, our knowledge of the significance of these compounds, their range of occurrence within the group, and their relation to pigmentation and other properties of the animal, remains both scanty and confused. This work was undertaken primarily in order to investigate the chemistry, metabolism, and function of vanadium in the organism, but it has been found necessary, if any correlation was to be made between these results and those of earlier workers, to make in addition certain purely histological observations on ascidian blood. It may be confessed at the start that it has been found impossible to suggest any plausible explanation of the function of the vanadium compound, and that only a little progress has been made towards elucidating its chemical nature. The real purpose of this paper is to clear away a number of misconceptions that have gathered round the subject, and by a critical review, in the light of experiment and observation, of the findings of previous authors, to consolidate such information on the subject as is available.