Aug. i, 1921 
Studies in the Physiology of Parasitism 
623 
deactivation of the enzym was very rapid, and below 45 0 its action was 
retarded. Experiments with the ground hyphae in which 0.25-gm. lots 
were suspended in 25 cc. of distilled water and exposed to the same 
temperatures as the solutions discussed above gave similar results. 
In recapitulation it may be said that the intracellular and extracellular 
pectinase bear the same relation with respect to the optimum tempera¬ 
tures for maceration. 
SUMMARY 
(1) Rhizopus tritici produces a powerful intracellular and extracellular 
pectinase when grown in sweet-potato decoction. 
(2) The enzym is able to effect the complete maceration of raw sweet- 
potato disks so that coherence of the cells is entirely lost. 
(3) The optimum temperature for maceration is between 45 0 and 55 0 C. 
At 6o° deactivation of the enzym is nearly instantaneous; below 45 0 
tlie activity of the enzym decreases simultaneously with the decrease in 
temperature. 
(4) The maximum enzym content of the hyphae and the solution is 
attained in about 24- and 48-hour-old cultures, respectively. 
(5) The volume of the enzym solution of a given strength does not 
influence the rate of maceration; the concentration of the enzym in the 
solution does. 
(6) Exposure of the hyphae for 2 hours to direct sunlight does not 
affect its macerating power. 
(7) Centrifuging to remove the sand and fungous debris slightly deacti¬ 
vates the enzym. 
(8) Filtering the solution in which the powdered hyphae and sand are 
suspended through filter paper weakens the enzym; filtering the solution 
after the removal of the fungous felt does not reduce its strength. 
(9) Extraction of the powdered hyphae for 18 hours in water does not 
increase the rate of maceration when compared with hyphae not ex¬ 
tracted. 
(10) Toluol may safely be employed as an antiseptic without impair¬ 
ing tlie action of the enzym. 
(11) The quantity of sand used for grinding the hyphae does not 
influence the action of the enzym. 
(12) The treatment of the hyphae with acetone for 12 minutes and 
ether for 3 minutes has no influence on the macerating action of the 
hyphae. 
(13) Washing the hyphae in running water for 15 minutes has no 
influence on the action of tlie enzym. 
(14) The results of these investigations indicate that work of this type 
involving a study of the relationship existing between a host and its 
parasite may throw some light on the important question of parasitism. 
