356 WATER AND DISEASE 



milk supply, the sewage disposal system, the markets, the back 

 alleys, the dairies, or anything else. He goes directly to the bedsides 

 of the patients. Of course he must obtain the names and addresses 

 of the patients from someone from the local health officer, if he 

 has them; from the attending physician, if the health officer has 

 no list; from the lay citizens themselves, if no one else is immediately 

 available. The more complete the list, the faster he can work, 

 because then he is not compelled to hunt up the cases personally. 

 But if there be no list, he begins making one himself. His inten- 

 tion is to see just as many patients as he can, for each furnishes evi- 

 dence and he wants it all. But he knows that it is not always 

 necessary at this stage to see absolutely all the patients, so long 

 as he sees the majority. 



"Reaching the patient's bedside, his investigation begins. 

 Automatically, almost mechanically, he decides whether or not 

 the patient has typhoid fever or not. Satisfied on that point, 

 his first question is not, 'Tell me all the different water supplies 

 you have used, or all the sources of milk you have used.' The 

 first question is, ' When did you first show the earliest symptoms of 

 the disease?' Why? Because this date once fixed, at which infec- 

 tion entered the patient's mouth is fixed also, i. e., a date between 

 one and three weeks previous to the date of the earliest symptoms. 

 Remember that at that stage the detective may not have even an 

 inkling as to which of the usual factors water, milk, food, flies 

 or fingers is involved. Still less can he guess which particular 

 water supply, milk supply, etc., of the many possible ones, may be 

 the guilty one. But the answer to this question reduces possi- 

 ble routes to those used by this patient not at any time but during 

 a specific period, i. e., from one to three weeks preceding his date 

 of earliest symptoms. 



"Not yet, however, are the milk and water questions offered. 

 The second question is 'Where were you during that period?' 

 Why? Because if the patient were not in the community during 

 that period, he could not have contracted his infection within it, 

 ;nid does not belong to the outbreak under examination at all but 

 to some other. He is in brief an 'imported case/ and while, of 

 course, he is to be supervised lest he spread his infection to others, 

 he cannot help to locate the source of the main outbreak unless 

 perchance he be himself that source, i. e., the introducer to the 

 community of the original infection. If he be an imported case 

 he is noted for further reference and the detective goes to another 

 patient. If not, the questions continue. But not yet is water 

 or milk or flies mentioned. The third question is, 'Were you asso- 

 ciated during your period of infection with any then known typhoid 

 case?' Why? Because such association, especially if intimate, 

 makes it more probable that the case under examination received 



