12 INFLUENCE OF FOOD PKESEKVATIVES ON HEALTH. 



statement in detail as to the manner in which they used tobacco, the 

 kind and amount used, and times of day when used. They then 

 pledged themselves to continue the use of tobacco in exactly the same 

 way, in the same quantities, and at the same times during the whole 

 of the observation period. In this way any effect which the use of 

 tobacco might have upon health and digestion would be uniform 

 throughout the whole period of observation, and therefore would 

 not influence the data relating to the use of preservatives and coloring 

 matters. 



NUMBER OF PERSONS SELECTED. 



Mention has already been made of the differences between species 

 of animals in regard to digestive processes. In the same species of 

 animal, however, marked idiosyncrasies exist among different individ- 

 uals in relation to kind of food and rate and degree of digestion. 

 These idiosyncrasies in the human animal are often accentuated, and 

 failure to consider them might lead to a grievous error in the inter- 

 pretation of analytical data. To eliminate, so far as possible, the 

 effect of any idiosyncrasy, it was deemed advisable to select as many 

 candidates as possible for the purpose of experiment. The facilities 

 of the kitchen, the dining room, and the laboratory were carefully 

 considered, and the decision was reached that 12 persons would be 

 about the- maximum number which could be placed under observation. 

 When the quantity of analytical work connected with an experiment 

 of this kind is considered, it is evident that only with a very large 

 laboratory and a great number of assistants could work with more 

 than 12 be property conducted. 



CONTROL OF MEMBERS OF THE TABLE. 



The 12 persons chosen for the table were selected in harmony 

 with the .principles above described and were fully instructed in regard 

 to the nature of their duties. Since it was not advisable to keep them 

 under continual observation, it was arranged that half of them should 

 be under observation and the other half should be left at liberty to 

 pursue their usual habits of life, conforming, however, as nearly as 

 possible, to the methods of living which they would follow when under 

 observation. Thus the time of relaxation in each case was equivalent 

 to the time of observation. In fact, the nature and extent of the work 

 which the members of the table would be called upon to do were fully 

 explained to them before they were asked to sign the pledges neces- 

 sary to place them under the self-restraint which the character of the 

 work required. This having been arranged, each of the members of 

 the table subscribed to the following pledge: 



I hereby agree, on my honor, to follow implicitly the rules and regulations gov- 

 erning the hygienic table of the Bureau of Chemistry during the time that I am a 



