The sympathetic law of contagion "...holds that things that have once been in contact with one another may influence or change each other for a period that extends well past the termination of contact...once in contact, always in contact." (Rozin and Nemeroff 1990: 206). The central idea of contagion is that an "essence" is potentially transferred from a source to a recipient, often through some form of medium (Rozin and Nemeroff 1990: 208). Rozin and Nemeroff identify four varieties of contagion; forward as opposed to backward contagion, and positive versus negative contagion (1990: 208). The similarities between "microbial contamination" and the law of contagion are most evident in the process of forward contagion, where "...an essence from the source reaches the recipient, either directly or [through] a medium, and exerts some effect on the recipient." (Rozin and Nemeroff 1990: 208). Backward contagion reverses the order of causation (Rozin and Nemeroff 1990: 208), occurring when an essence is transferred to a recipient via some item, which "...is usually possessed rather than incorporated by the recipient." (Rozin and Nemeroff 1990: 208). The essence filled item is manipulated (often damaged) "...with the intent that the source itself will be similarly damaged." (Rozin and Nemeroff 1990: 208). Positive contagion involves a favorable or desirable reception of essence, while negative contagion predictably involves the reverse case, and seems to be most prevalent (Rozin and Nemeroff 1990: 208-209), at least in so far as Rozin and Nemeroff were particularly concerned with disgust-responses. So what then do Rozin and Nemeroff offer as examples of sympathetic contagion? Consider the following text:

From a contagion perspective, the world is suffused with essences; footsteps, money, clothing, all foods, and many other items bear the residues of insects and other people, savory or unsavory. The most neutral object may become highly charged (usually negatively) if we contemplate its history. And yet, neither we, nor the much more contagion-sensitive Hua, are crippled by this prospect. How is this managed? (Note that we again revert to negative contagion in this discussion) We put all but the most salient instances of contagion out of our minds; we frame situations so as to reduce the salience of past history. We do not think that the air we breathe during a ride on public transportation or at a lecture was just exhaled by our neighbors (unless it is called to our attention by an unsavory odor). We do not think of the history of the money we handle, or where our dog’s face has been as he licks us. We also arrange, sanitize our environment to make personal and offensive linkages less salient. Food is purchased at supermarkets in sanitized packages, as if processed by machine. In this context, it is inappropriate to think about WHO prepared the food. In U.S. culture it is primarily the obsessive who worry excessively about cleanliness and past history, and who become crippled on this account. There have been situations at other times, and in other cultures, where contagion has become crippling. In 18^th and 19^th century France, there was excessive concern of corruption via inhaled air. Disinfection, deodorization, and ventilation came to be of major importance (Corbin 1986). Fear or sorcery via contagion may become extreme. Frazer…reports that among the Betsileo of Madagascar, "blue blood" or ramanga have the job of eating all nail pairings and licking up all spilled blood of nobles to prevent sorcery. They follow their masters around to dispose of residues (Rozin and Nemeroff 1990: 218).