BACTLLVS TYPHOSUS. 419 



the test-tube reaction a larger amount is needed ; this 

 may be obtained from blood drawn from a superficial 

 vein by means of a hypodermic syringe, or from the 

 cleansed skin by a wet-cup, or, better still, from a 

 small cantharides blister. 



It is proper to state, however, that occasionally cult- 

 ures of genuine typhoid bacilli are encountered that do 

 not respond to this peculiar influence of typhoid blood, 

 even though the blood be tested at diiferent stages of 

 the disease, and even though it causes the characteristic 

 cessation of motion and clumping with other cultures of 

 this organism upon which it may be tried. 



When employed conversely — i. e., for deciding if 

 the serum used is from a case of typhoid fever or not — 

 the reaction constitutes "Widal's serum diagnosis of 

 typhoid fever." For this purpose it is often necessary 

 to test several cultures of genuine typhoid bacilli, from 

 different sources and of varying degrees of vitality, be- 

 fore a culture is procured that gives the reaction most 

 conspicuously and quickly with genuine typhoid serum. 

 This culture is then to be set aside, to be used for this 

 test with serums from doubtful cases of the disease. 



Widal's Reaction with Dried Blood. — For clin- 

 ical purposes it is of importance to know that this reac- 

 tion can be obtained from dried blood — i. e., by the 

 method suggested by Wyatt Johnston, of Montreal. 

 In this method a drop of the blood to be tested, ob- 

 tained by a needle-prick in the cleansed finger or lobe 

 of the ear, is collected on a bit of clean, unglazed 

 paper and allowed to dry. The paper is then folded, 

 kept free from contamination, and taken to the labora- 

 tory. With a medium-size platinum-wire loop a drop 

 of sterile bouillon, water, or physiological salt solution 



