31 
1889 - 90 .] Dr G. E. C. Wood on Enzyme Action. 
exhibit a varying susceptibility to acid reaction precisely as the 
organisms themselves do. This does not indicate that the organisms 
are more susceptible to acidity, according as their enzymes are more 
sensitive to its presence, but that the protoplasm as a whole, and 
with it the enzymes, is adapted to a certain set of conditions — its 
usual environment. 
This correspondence between the conditions under which the 
organism exists and those under which the enzymes act, is exhibited 
even more strikingly by a consideration of their temperature relations. 
Every enzyme has an optimum temperature at which it works most 
effectively, and a lower and a higher limit at which it ceases to act. 
In the case of the cold-blooded animals this optimum temperature 
is much lower than in the warm-blooded animals. Fick * and 
Murisierf found that the gastric juice of the frog, pike, and trout 
dissolved albumen at 0° C. Hoppe-Seyler J has confirmed this 
result, and states in addition that at higher temperatures they did 
not act so effectively as at moderate temperatures. The gastric juice 
of a mammal, on the other hand, peptonises best at the temperature 
of the body, 39° C., and becoming less active at lower temperatures, 
is finally inoperative at 10° C. Again, while the diastatic ferment of 
the pancreas and saliva acts best between 37° and 40° C., that of germ- 
inating barley, where the temperature is usually much higher, has its 
optimum at from 54° to 63° C. Micro-organisms exhibit even greater 
differences as regards the temperature to^ which they are adapted ; 
some grow and liquefy the gelatine at 0° C., and as is seen in the case 
of the micrococcus, which causes the phosphorescence at sea, can at 
this temperature exhibit their characteristic action ; § others do not 
grow at a temperature under 50° C., and at70°C. continue to vegetate 
actively.|| In accordance with the adaptation of the organism as 
regards temperature, the liquefaction of the gelatine, occasioned by 
a microbe, may vary greatly, even to the point of cessation, with 
the temperature; but how far this is due to lessened production 
of the enzyme, and how far to its action being interfered with, 
* Arbeiten Physiol. Lab. Wurzburg, ii. p. 181. 
t Verhandlung. d. phys. med. Ges. in Wurzburg, Bd. iv. p. 120, 1873. 
X Pfliiger's Archiv, Bd. xiv. p. 395, 1877. 
§ Forster, Central./. Baht., 1887, vol. ii. No. 12; Fischer, Central, f. 
Baht., 1888, vol. iv. No. 3. 
!| Globig, Zeit. fiir Hygiene, vol. iii. p. 295. 
