It is now almost universally recognised that a test for disinfectants which is to yield results of direct practical significance must include appropriate “organic matter” in the test mixture. Some types of disinfectant, notably those which act by liberating chlorine or oxygen, are greatly reduced in activity by the addition of only small quantities of any extraneous material with which these elements can combine. Other disinfectants are more resistant to this influence; they are capable of efficient action in the presence of excreta and dirt of other kinds if used in adequate concentration. What this concentration should be under such unfavourable conditions it is necessary to determine, since the degree of interference is not the same for all disinfectants even in the same class, and no constant relationship exists between efficiency under these conditions and that displayed in a medium of distilled water as determined by the Rideal-Walker test. Numerous efforts have been made in the past to introduce tests employing adequate amounts of complex organic matter; few of these have achieved permanence and none popularity. The following short survey of past work is concerned only with what may be termed “excremental” disinfectants; the testing of surgical disinfectants, which may reasonably be held to demand different methods, is outside the scope of this paper.