549 
Enzyme of Nepenthes (II). 
On comparing the results of a, h, and c, it would appear 
that treatment with I °/ o Na 2 C0 3 for one hour at a tempera- 
ture of 5 o°C. is an approximate index to the stability of 
the enzyme. 
Filtration. It occurred to me that some light might be 
thrown upon the bacterial explanation of the digestive activity 
of the pitcher-liquid by experiments with liquid which had 
passed through a Berkefeldt-filter. I found that liquid which 
has passed through such a filter has lost its acid reaction 
and its colouration. It still retains some digestive power, 
but is far less active than unfiltered liquid, the period of 
digestion being more than doubled. 
This result might be made use of by the supporters of the 
bacterial explanation, as affording some sort of evidence in 
favour of that view ; but even so, it would be far from con- 
clusive. However, in order to test the value of this evidence 
I instituted some experiments with regard to the effect of 
filtration through the Berkefeldt-filter upon liquids containing 
pepsin and ptyalin. With regard to pepsin, I found that 
an unfiltered solution of glycerin-extract of pig’s stomach 
digested *05 grm. of fibrin in a quarter of an hour, whilst an 
equal quantity of the same solution after filtration required 
nearly 5 i hours to digest the same weight of fibrin. 
Similarly some diluted saliva caused the complete conversion 
of a small quantity of starch into sugar within a few minutes, 
whereas starch treated with filtered dilute of saliva continued 
to give more or less marked blue-reaction with iodine for 
four or five hours. 
It is clear that solutions of pepsin and of ptyalin are 
affected by the Berkefeldt-filter in much the same way as is 
the pitcher-liquid of Nepenthes. If it be argued that the 
diminished activity of filtered pitcher-liquid is due to the 
removal of Bacteria, the same argument must equally apply 
to the solutions of pepsin and of ptyalin ; but I do not think 
that any one would venture at present to attribute the action 
of gastric juice or of saliva to the presence of Bacteria. The 
obvious conclusion to be drawn from these experiments is 
