CONTROL OF INFECTIOUS DISEASES 767 



the culture prove negative the contact, whether immune or not, may 

 be set free because, since he is not infected, he will not become sick 

 himself nor can he give the disease to others. If it prove positive, the 

 contact, whether immune or not, is dangerous, even though not sick, 

 and should be isolated as dangerous; many physicians advocate giving 

 a prophylactic dose of antitoxin (1000 units) to prevent the develop- 

 ment of the disease in such contact. This dose ensures the non-develop- 

 ment of the disease for two weeks, at which time it must be renewed if 

 protection is still desired. Prophylactic doses, indeed, even therapeu- 

 tic doses (10,000 to 50,000 units), do not affect the bacilli themselves, 

 and therefore the infected contact who has been protected against 

 the disease by antitoxin so far as his own health is concerned, never- 

 theless remains a menace to others so long as the bacilli remain in nose 

 or throat. The practice of releasing an infected contact as soon as he 

 is immunized is illogical, unjustifiable, absurd and dangerous. Simi- 

 lar tests of nose and throat (by smears instead of culture) may be made 

 in the case of Cerebro-spinal Meningitis, the handling of the contacts 

 and the conduct of release or isolation being similarly carried out on 

 the basis of the results. Immune contacts (unless determined to be 

 infective as above) may be released at once, after disinfection of their 

 hands; and should be warned against the dangers of acquiring and 

 carrying the infection on their hands (in poliomyelitis, cerebro-spinal 

 meningitis, influenza, and diphtheria, in their throats and noses also) 

 as a result of further contact with the case, or with carriers. 



Non-immune contacts should be questioned carefully as to their 

 dates of contact with the case; and the dates of infectiveness of the 

 patient should be compared with these, in order to determine when the 

 exposure began and when it ceased. If minute enquiry of this kind 

 cannot be made, or is unsatisfactory for any reason, it is proper to 

 assume, until proved otherwise, that members of the same household, 

 office, etc., were all exposed on the first day the case became infectious, 

 ard continued to be exposed daily up to the date of isolation of the case. 



Whether exact individual determinations of these dates of exposure 

 be made, or the blanket assumption indicated be applied, the further 

 calculations are as follows: To the date of first exposure (usually the 

 date of onset in the patient) add the minimum incubation period of 

 the disease in question : this will indicate the earliest date at which any 

 infected contact can develop the disease and therefore the beginning of 



