McCarrison is credited with being the first to experimentally demonstrate the effect of deficient dietaries upon animal tissues and organs.[11] He also carried out human experiments aimed at identifying the cause of goitre, and included himself as one of the experimental subjects.[12] Much of McCarrison's work was pioneering. His 1921 book Studies in Deficiency Disease was considered notable at the time, being published at a time when knowledge of vitamins and their role in nutrition was crystallizing.[13] McCarrison himself noted that prior to publication of his studies on the pathogenesis of deficiency disease "no systemic post-mortem examination of animals fed on food deficient in vitamin B had ever been made; the histopathological effects of such food on the various systems of the body were wholly unknown; above all, its effects on the gastro-intestinal tract and the organs of digestion and assimilation, and the significance of these effects for clinical medicine, were wholly unsuspected