These recrudescences may be provoked by a very large number of disparate naturally-occurring stimuli, such as the common cold (hence "cold sore"), fever (hence "fever blister"), menstruation, administra tion of vaccine, emotional stress, trauma, severe sunburn, allergic re actions, chemical irritants, secondary dentition, coitus and digestive disturbances (Schmidt and Rasmussen, 1960). Recrudescences may also be provoked in the human patient by artifi cial stimuli. Some years ago it was the vogue to treat certain clinical conditions by artificially elevating the patient's temperature. It was noted in one study that when this was done Herpes simplex virus type 1 vesicles recrudesced in 46.2% of the patients (Warren et al., 1940), a high figure which serves as additional evidence of the pervasiveness of this infection in the human being. Similar results were obtained by Keddie et al. in 1941. In addition, it has been recorded that active in fection may recrudesce in the human patient after a renal transplant (Montgomerie et al., 1969), but which of all the various factors involved in such a procedure, including surgical shock and immunosupression, has caused the recrudescence is not known. The recrudescence of active Herpes simplex virus infections after surgical manipulation of the tri geminal ganglion will be discussed in a later section. Recrudescence of active infection has also been noted in laboratory animals which had been artificially infected with the virus some time earlier. In the rabbit. Good and Campbell (1945, 1948) noted that anaphylaxis provoked a recrudescence which manifested itself as a herpetic