the J er it salem Artichoke {FI eli ant hits tuber osus). 229 
The conditions of the activity of this inuhn-ferment are 
similar to those which govern the digestive ferments of the 
animal organism. Like saliva it works best in a neutral 
medium. The presence of a very slight trace of acid does it 
no harm ; in fact it is rather advantageous. The sap expressed 
from growing tubers is very faintly acid, the acidity being 
equal to about *ooi per cent, of HC 1 . Stronger acids than 
this are prejudicial, and exposure for an hour to an acidity 
equal to *2 per cent, of HC 1 at a temperature of 40° C 
destroys it altogether. Alkalis are similarly hurtful, no fer- 
ment-power surviving an exposure for an hour to a strength 
equal to 1*5 per cent, of Na 2 Co 3 solution. The rapidity with 
which the destruction of the ferment by acid takes place is 
dependent on the temperature at which it is kept during the 
time the two are in contact. At a low temperature it is much 
less affected than at 40° C, but after an hour’s exposure at 
10-15° C its working power is very much impaired. 
The energy of the ferment shows the same variation with 
the temperature, being much greater at 40° C than at the 
ordinary temperature of the soil in which its normal action 
takes place. The same thing I have noted elsewhere 1 is the 
case with the proteolytic ferment occurring in the lupin. It 
is destroyed by boiling. 
The products of the action of the ferment on inulin are a 
sugar and an intermediate body possessing properties which 
resemble those of inulin on the one hand and sugar on the 
other. In the first stages of this investigation, formation of 
sugar was, as already indicated, taken as the sign of the 
activity of the ferment extracts. The products of the diges- 
tion were collected later for more exact enquiry into their 
composition. To obtain them digestions were conducted for 
some days in dialysers ; the first three days’ dialysates were 
rejected, to be sure that whatever was examined was really the 
product of the ferment’s action and not any dialysable matter 
possibly mixed with the inulin ; the later dialysates were 
1 Phil. Trans., vol. 178 B, p. 46. 
