226 Ortho-Tolidin as Indicator for Occidt Blood [Jan. 



Guaiaciim and benzidin, when positive, gave prompt reactions 

 but in very dilute Solutions the color faded quickly. o-Tolidin de- 

 veloped the greenish-blue, or deep blue, more slowly but the color 

 persisted for some time, even several hours. 



The results of the comparative tests are briefly summarized 

 below. 



{i) In urine: Guaiacum and benzidin detected blood, i in 6000; 

 benzidin was slightly the more sensitive reagent; o-tolidin detected 

 I in 24,000; phenolphthalin, less than i in 2,000. 



(2) In feces: Feces of patients on a meat-free diet for seven 

 to ten days vvere used and a 2 per cent. emulsion prepared. Guaia- 

 cum detected blood, i in 10,000; benzidin and o-tolidin, i in 100,- 

 000, the tolidin reaction being slightly slower but persisting — the 

 benzidin color fading quickly in very dilute Solutions; phenol- 

 phthalin gave reactions only when dilutions did not exceed i in 

 2,000. 



(3) In stomach contents: Stomach contents after ordinary test- 

 meals were employed. One c.c. of stomach contents was added to 

 the reagent before the diluted blood Solution was introduced. 

 Guaiacum detected i in 5,000; benzidin and o-tolidin, i in 30,000; 

 phenolphthalin, even after the acidity of the stomach contents had 

 been neutralized before applying the Solution, was less delicate than 

 guaiacum. 



Experiments were conducted to determine the keeping properties 

 of the reagents. Although benzidin and o-tolidin are about equal 

 in delicacy for blood in feces and stomach contents, the delicacy of 

 the benzidin reagent diminishes 50 per cent. in 24-36 hours, while 

 o-tolidin will remain unchanged in delicacy for from three to four 

 weeks. 



o-Tolidin is as sensitive a reagent for occult blood in stomach 

 contents and feces as benzidin. Its action is less inhibited by urine 

 than any of the other reagents. Its Solution in acetic acid can be 

 kept for one month without its delicacy being reduced. After that 

 its value decreases slowly. Benzidin'* Solutions in acetic acid cannot 

 be kept twenty-four hours without very serious deterioration in deli- 

 cacy; some preparations decreasing over 50 per cent. 



* Three different products were compared. 



