1905] CALDWELL—ACTION OF BROMELIN 415 
While there are a number of exceptions, these results show a general 
agreement which is more striking in view of the total lack of harmony 
in the earlier work with poisons, whether with plants or animals. 
Silver, mercury, and copper stand at the head of the three lists. In 
my experiments, cadmium stands near zinc, nearly in the place it 
should occupy in accordance with the theory of MATHEWs, who 
found it in his work only less poisonous than copper. MATHEWS 
and McGuiGan have found sodium less poisonous than lithium or 
strontium, using the chlorids. I find the three sulfates practically 
equal in toxicity, while sodium nitrate is much more poisonous than 
the other nitrates. My results agree more nearly with those of 
Martuews in the places given lithium, lead, and cobalt. The great 
toxicity of barium in my experiments cannot be attributed to impuri- 
ties in the salts used or to inaccuracy in performing the experiments, 
since several standard preparations gave markedly uniform results, 
and the series has been worked over so many times that the possibility 
of mistake is excluded. 
The nitrates uniformly inhibit the action of the enzyme in some- 
what greater dilution than the corresponding sulfates and chlorids, 
which agree very closely. 
The action of the enzyme is markedly weaker and is uniformly 
inhibited by poisonous solutions of less concentration than when 
acting in alkaline media. This confirms the evidence already given 
for the existence of two enzymes. 
EXPERIMENTS UPON AUTODIGESTION. 
The experiments upon autodigestion were suggested by the dis- 
covery that while none of the tests for peptones, leucin, or tyrosin 
were given by freshly prepared aqueous solutions of the impure 
enzyme, all these were present in such solutions after standing for 
a little time at 25-60° C. CHITTENDEN (loc. cit.) has stated that the 
proteids of the juice are exceedingly resistant to the action of the 
enzymes, while VINES (25, ¢) has mentioned the occurrence of auto- 
digestion in the expressed juice. My own observations led to the 
supposition that the associated proteids were acted upon by the 
enzyme at suitable temperatures. This was found to be true of acid 
and alkaline solutions, not of neutral ones. The associated proteid 
