Il8 BACTERIOLOGY 



cutaneous reaction of Von Pirquet and of Moro are the 

 safest and most dependable. They are especially accu- 

 rate in children. The ophthalmo-reaction is less reliable 

 and is attended with some danger to the eye, especially 

 should there exist some previous inflammatory condition 

 of that organ. 



It may be noted in passing that the tuberculin test 

 affords a most efficient means of recognizing tuberculosis 

 hi cattle, and is, therefore, of signal importance in efforts 

 to obtain a tuberculosis-free milk-supply for cities and 

 institutions. 



THE VIDAL TEST FOR TYPHOID FEVER 



The Widal (or agglutination) test for typhoid fever 

 has been referred to before in this work. It depends 

 upon the presence in the blood of a typhoid patient at a 

 certain stage of the disease of substances termed agglu- 

 tinins, which when brought in contact with living ty- 

 phoid bacilli cause them to clump together and cease their 

 ambulatory movements. It is evident, therefore, that 

 the infection must have been present a certain length 

 of time for the Widal test to be positive, that is, until 

 sufficient time has elapsed for the agglutinins of the 

 typhoid germ to have been elaborated in the blood of the 

 patient, or the Widal test will be negative. We find, 

 therefore, that the test is of no practical value until after 

 the first week of the infection. The test is also uncertain 

 because of the fact that the blood of many normal per- 



