768 MICROBIOLOGY OF DISEASES OF MAN AND DOMESTIC ANIMALS 



quarantine (or observation) necessary for such contact or contacts. 

 To the date of last exposure (usually the date of isolation of the patient) 

 add the maximum incubation period of the disease plus the maximum 

 prodromal period, thus fixing the last day on which any contact will 

 develop the typical symptom of disease and hence the end of the neces- 

 sary quarantine (or observation) period. Theoretically the maximum 

 incubation period would be sufficient but the prodromal period is in- 

 cluded in practice beca'use, in many diseases, the onset may be trivial 

 and may therefore be overlooked, the contact being discharged just as 

 he begins to be infective; if the full prodromal period be included, the 

 most careless can hardly fail to observe that the disease was begun 

 and that isolation must be carried out. 



In those diseases where the incubation period is long, and is not in- 

 fectious (for example, in mumps), there will often be found to exist a 

 period after isolation of the original patient and before the first contact 

 can become sick, of a week or even ten days or so. During this period 

 non-immune contacts may be given interim permits, allowing them to 

 go on with their usual lives up to the date when the first case may be 

 expected to develop. On that date they should be quarantined (or 

 placed under observation) for the necessary period. 



In measles, and German measles similar methods may be followed. 

 In Diphtheria and Scarlet Fever it is rare that the time so saved to the 

 contact is long enough to be worth the extra risk and work involved. 



OBSERVATION VERSUS QUARANTINE 



In dealing with intelligent conscientious people, or with people 

 under full control as in schools, armies, etc., non-immune contacts, if 

 observed twice daily by competent medical men or nurses, throughout 

 the period during which they may develop the disease, may be freed of 

 all other quarantine restrictions. The family physician will generally 

 cooperate with the Health Officer in this twice-daily inspection, thus 

 saving much otherwise necessary restriction, to the great satisfaction 

 of all concerned. 



The quarantine periods and examples of calculations are appended. 

 See Table. 



