Bitter Pit. 343 



0.001 % at 28° and 35° C. With larger amounts of tannic acid an 

 apparent acceleration may be shown, but this is simply due to the 

 tannic acid condensing and precipitating the starch, so that the 

 liquid above gives yellow with iodine. If the whole of the j-emain- 

 ing starch is precipitated with excess of tannic acid, filtered, dried 

 and weighed, the control always contains less starch than the tube 

 with tannic acid. To get the full retarding action, the diastase 

 extract must contain no proteids capable of combining with and 

 removing the tannic acid, and for this reason filtered malt diastase 

 is more sensitive to the presence of tannic acid than unfiltered malt 

 diastase. When the diastase extract is free from proteids capable 

 of removing tannic acid, the retarding action is probably entirely 

 due to the action of the tannic acid on the starch and not to an 

 action on the diastase. In addition, I was able to show that dilu- 

 tions of metallic poisons unable to destroy either oxidase or diastase 

 were still poisonous to the living protoplasm of the apple and potato 

 when applied externally. It is, in fact, a fairly general rule that 

 enzymes are a little more resistant to dry and moist heat and to 

 poisons than the protoplasm of the cells containing them, and hence 

 the diastase method will only detect a poison when present in 

 relatively large amount and in soluble form, and even then only 

 when nothing else which affects diastatic action is present in the 

 tissue. 



At the Sejitember meeting of the Royal Society of Victoria. 

 Rothera, together with Miss Kincaid and Miss Jackson, advanced 

 a criticism of my work on the sensitivity of apples to poison. They 

 stated that the poisoning effects obtained by me were not due to the 

 poisons used at all, but to the action of the distilled water to which 

 the apple pulp was exposed at the points where the cuticle had been 

 removed. They based this conclusion on the following statements : 

 — (1) Prepared apples floated on distilled water developed brown 

 pits beneath the points from which the "cuticle" had been re- 

 moved. (2) In isosmotic (isotonic) solutions of sodium chloride 

 (2.6 % and upwards) to which poisonous solutions were added, no 

 brown pits developed. (3) Peeled apple pulp floated on distilled 

 water slowly turns brown, but remains colourless when floated in 

 apple sap. They conclude, therefore, that in (2) and (3) the pulp 

 cells are under normal osmotic conditions, and the pulp cells remain 

 living, and that in (1) they are under abnormal osmotic conditions 

 and therefore die. As a matter of fact the reverse is the case. No 

 plant cell provided with a cell-wall can grow in a medium isosmotic 



