33 
the organism. He is of the opinion, therefore, that their physiological 
role both in animals and plants is one of defense against invasion by 
micro-organisms. In this connection Sieber ( 402 ) has shown that the 
oxidases have the power of destroying toxins. According to her 
observations, the fibrin of the blood of a normal horse gives no oxidase 
reactions, whereas the fibrin obtained from the blood of a horse im- 
munized against diphtheria gives a blue coloration with guaiacum, 
indicating the formation of oxidases in the blood as the result of 
immunization. As we shall see, one of the oxidases, tyrosinase, is the 
active agent in the production of melanins, and hence of profound sig- 
nificance in its relation to certain pathological conditions of melano- 
genesis in man. In this connection Hougonenq and Paviot ( 22 °) claim 
to have found that certain malignant tumors give the guaiacum reac- 
tion. Still other facts of interest, pertaining to the occurrence of the 
oxidases or to their mode of action, are set forth in the following pages. 
THE GUAIACUM REACTION. 
Our first knowledge of the oxidizing ferments is closely associated 
with what is known as the guaiacum reaction, viz, the production of a 
blue coloring matter when gum guaiacum or its tincture is treated 
with certain oxidizing agents. According to Binz ( 68 ) our knowledge 
of guaiacum dates back to the sixteenth century when in 1508 it was 
first imported into Spain from Santo Domingo as a remedy for syphilis 
by Consolvus Ferrand, himself a syphilitic, soon after which it 
became known all over Europe as an antisyphilitic. {See Mono- 
graph of Ulrich von Hutten, De Guajaci Medicina et Morto Gallico; 
Liebermann, Mainz, 1519, p. 74). 
That guaiacum resin becomes bluish-green in color on standing in 
the air and light and the liquid around the stoppers of bottles con- 
taining tincture of guaiacum generally acquires a bluish-green color 
are matters of everyday experience to those who have ever had occa- 
sion to use these substances. In 1804 Wollaston ( 461 ) was the first to 
show that this color change on the part of guaiacum is brought about 
by the air under the influence of light. According to this author, 
rays of light which cause the emission of oxygen by silver chloride 
cause its absorption by gum guaiacum. A few years later William 
Brande ( 94 ) showed that guaiacum becomes blue in pure oxygen gas 
more rapidly than in air. 
Shortly afterwards a number of interesting observations on the 
bluing of guaiacum were made by the French pharmacists. Thus it 
was pointed out by Boullay( 73 ) that a mixture of simple sirup, dis- 
tilled water, gum arabic, and tincture of guaiacum takes on the 
color of a suspension of verdigris, and further that certain dentifrices 
containing guaiacum, when taken into the mouth, become intensely 
blue or green. This change of color had been attributed to impuri- 
11670— Bull. 59—10 3_ 
