52 Mr. H. Onslow. 



alcohol. The aqueous solutions of these precipitates were powerless to 

 inhibit an active tyrosinase solution. 



Experiment VI: The Absence of Tyrosinase in Recessive White Rabbits. — The 

 extract from recessive white rabbits (prepared as previously, see above) was 

 added to each tube. 



No. 



Substance added. 



Appearance after 12 hours. 

 Without H 2 2 . | With H„0„. 



1 



None 







2 



Tyrosine 







3 









4 









+ indicates positive reaction. 

 — indicates no change. 



This experiment clearly shows that the extract from recessive white 

 rabbits not only lacks a tyrosinase but also an enzyme capable of oxidising 

 ^>-cresol or adrenalin, although Meirowsky* reports the presence of an 

 adrenalin-oxidising enzyme in extracts from the normal human skin. The 

 results obtained with white mice and the white areas of the Dutch rabbits 

 were similar in all respects to those given by the recessive white rabbits in 

 Experiments V and VI, and clearly show that recessive whiteness is due to 

 the absence of at least tyrosinase, and possibly of chromogen as well. 



3. The Effect upon the Shin Extracts of Dihydroxyphenols. 



The presence of what might possibly have been a second specific enzyme, 

 with properties differing from those of tyrosinase, was observed very early 

 in the course of the, experiments, but to avoid confusion the account of it 

 has been reserved until now. An experiment was performed to see whether 

 phloroglucin and similar dihydroxyphenols inhibited the reaction of tyro- 

 sinase in the manner described by Gortner.f 



Experiment VII: The Effect of the Extract from Black Rabbits upon 

 Dihydroxyphenols. — Ferment fluid (prepared as previously) and tyrosine were 

 added to each tube. 



* Meirowsky, 'Centralbl. fur allg. Path. u. pathol. Anat.,' vol. 20, p. 301 (1909) ; and 

 Miinchener Med. Wochenschrift,' vol. 58, No. 19, p. 1005 (1911). 

 t Gortner, 'Jour. Biol. Chemistry,' vol. 10, No. 2, p. 113 (1911). 



