The Novartis Foundation Series is a popular collection of the proceedings from Novartis Foundation Symposia, in which groups of leading scientists from a range of topics across biology, chemistry and medicine assembled to present papers and discuss results. The Novartis Foundation, originally known as the Ciba Foundation, is well known to scientists and clinicians around the world.

During the past decade there has been an increasing awareness of the need for a different approach to the problem of bilharziasis. We do know that 180-200 million people are infected and that the infection is increasing but we have not as yet been able to answer the question: Are they suffering from a disease. Study of vital statistics or hospital records, mass biochemical or immunological tests and community surveys have not yet provided the full answer. Gradually and perhaps begrudgingly, we have come to realize that we must study the ma- initially by means of well controlled clinical observations to obtain evidence for the altered physiology, if any, due to bilharzial infection; secondly and equally important through pathological studies on individual patients to determine the structural changes, if any, as a result of infection with this parasite; and by post mortem studies. Experimental studies of bilharzial infection in animals, valuable as they may be for the elucidation of the pathogenesis of the lesions in the laboratory animal and in man cannot serve as a substitute for the precise information on the nature of the possible lesions induced by bilharziasis in man. Basically, the significance of any clinical observation can 'be evaluated only through reliable pathological confirmation.

Infection by Schistosoma mansoni, S. haematobium, S. japonicum and more rarely S. mekongi and S. intercalatum