PHYSIOLOGICAL CHEMISTEY 



341 



is formed in the presence of blood. Ascertain in what dilution blood 

 gives this test. Ozonic ether and alcohol contain hydrogen peroxide. 

 The solution is first boiled to destroy any oxidising enzymes present. 

 These bodies can effect the same change, as also can many salts of 

 metals, such as copper, iron, gold, cobalt, strong sodium chloride 

 solution, and various other fluids such as milk, saliva, mucus, sweat, 



FIG. 228 Haemin. X1500. 



and juices of vegetable origin (extract of pea flour, fruit juices, etc.). 

 If, however, the solution be first boiled, in the absence of metallic 

 salts, the reaction is to be regarded as a reliable one for blood. In 

 any case, if the test be negative, most investigators regard it as certain 

 that Hood is absent. 



Other bodies such as aloin, benzidin, the leuco-base of malachite green and 

 phenol-phthalin can take the place of guiac. 



Aloin is said not to be so sensitive as guiac, benzidin is generally reported to 

 be more sensitive, but according to Kastle the most sensitive is phenol-phthaline, 

 with which he has detected 1 in 8,000,000 of blood. 



