184 MICROBES AND HEALTH. 



substance in sufficient amount to cause prompt and 

 marked reaction, the presence of a previous or existing 

 typhoid infection may be considered extremely prob- 

 able." Other requirements are named and the circular 

 states, if these are met: "The presence of a previous 

 or existing typhoid infection may, for diagnostic pur- 

 poses, be practically considered as established." The 

 circular also states: "The reaction is occasionally ab- 

 sent in cases of typhoid fever until the third or fourth 

 week, or even until convalescence is established." 



"Four weeks, or until convalescence!" It might be 

 interesting to know at what time convalescence makes 

 it appearance in those cases treated by the New York 

 Board of Health. 



In another place the circular states : "In those cases 

 in which the reaction is absent after the ninth day, it 

 may be reasonably assumed that the large majority will 

 not prove to be typhoid fever." 



In a paper by Dr. D. Murray Cowie, read before the 

 Ann Arbor Medical Club (Michigan), September 13, 

 1899, the author understands Dr. Cowie to say, that 

 the Widal reaction may occur thirty-seven years after 

 recovery from typhoid fever. 



On the New York circular there is printed in large 

 type : "Circular of information." Is it ? It says "as 

 a rule" the blood of typhoid patients between the fifth 

 day and the third or fourth week, or until convalescence, 

 contains a certain substance which gives the Widal test. 

 It also says the blood of persons suffering from other 

 diseases, and even those in health, may possess the same 

 properties as that of the typhoid fever patient. Again, 



