Abstract
The distribution of chromaffin tissue in the rabbit, frog and dogfish is described and compared with findings previously reported for the human foetus. The results are correlated with the adrenaline-noradrenaline content of the tissues. It is shown that in the dogfish, where the chromaffin tissue is completely separate from adrenocortical material, the pressor activity of the tissue is entirely due to noradrenaline. In man and rabbit the intra-adrenal chromaffin tissue contains a mixture of adrenaline and noradrenaline, whilst the pressor activity of the extra-adrenal chromaffin tissue (para-aortic bodies) is entirely due to noradrenaline. The para-aortic bodies of the human foetus are probably endocrine organs and may be concerned with the humoral control of vasomotor tone.