Towards the end of the 18th and the beginning of the 19th century an alteration occurred in Western thinking that allowed radical changes in many fields of study, including the life sciences.! Prior to this time, the study of nature was predominantly hermeneutic, concerned with classification and interpretation of" signs" that would show one the relationship of a plant or animal to its place in the universe (for example, its role in a medical cure). This perception of the order of reality persisted through the 18th century, until a new view emerged, in which underlying causes and proн cesses were examined. Thus, nature and life moved into the abstraction; the word biology was coined in 1800 by Burdach and extended in 1802 to the study of living bodies by Treviranus and again by Lamark. It was also at this time (1803) that the germ theory of disease first appeared (Med. J. IX, 484). In 1826, Fidele Bretonneau concluded that diseases are specific, develн oping through specific reproducing agents. Agostino Bassi (1836) isolated a parasitic fungus as the causative agent in a silkworm disease, and John Snow (1849) postulated similar agents operative in the communication of cholera. Pasteur began his studies in fermentation in 1854, which led to those studies that, together with those of Koch, resulted in the acceptance of the germ theory. Thus, disease came to be understood as an invasion of a healthy body by an infectious agent. Our understanding of immunology is firmly based upon this view. Alн though Pasteur generalized the vaccination procedure of Jenner to include