:U6 Alfred J. Eivart : 



When imiuersed in its own sap living pulp usually remains un- 

 browned for some time if the sap has been previously sterilised by 

 boiling. The soluble matters in this sap are impermeable to the 

 living protoplasm, just as they are when inside the cell. No pene- 

 tration therefore takes place, .and the tannic and other acids of the 

 sap prevent or retard the development of bacteria. Such pulp is, 

 however, readily invaded by fungal hypae. 



In all cases, for a poisoning effect to be exercised the poison must 

 be able either to penetrate the protoplasm or to injure its ecto- 

 plasmic membrane. A curious point worth noting here is that the 

 protoplasm of the pulp cells is, as one might expect, resistant to 

 tannic acid. This is probably due to the formation of an imper- » 

 meable coagulation film on the surface of the ectoplasmic membrane, 

 such as must exist normally on the endoplasmic membrane. This- 

 membrane appears to increase the impermeability of the protoplasm,, 

 especially to organic acids (malic, citric, tartaric, oxalic), and 

 hence in the presence of tannic acid externally applied, solutions 

 of these acids are only poisonous in considerably increased concen- 

 tration. This may explain the remarkable effectiveness with which 

 the delicate pulp cells retain their sugary and acid contents, al- 

 though some of the acids when applied externally are poisonous. 



It is perhaps hardly necessary to say that in my own work these 

 possibilities of error were detected early. Every experiment was 

 done with a control in distilled water. These controls were 

 unaffected, and, in fact, properly prepared apples can be kept 

 almost as well floating in distilled water as ordinary apples can be 

 kept in air. In addition the results were throughout consistent — 

 i.e., Avith increasing dilution less and less poisoning effect was 

 exercised. In order to settle this matter finally, I arranged to 

 perform these experiments before a committee consisting of Dr, 

 Hall, President of the Royal Society, Pi-ofessor Osborne, Dr. 

 Rothera, Miss Kincaid and Miss Jackson. All the apples were pre- 

 jjared by me. In the whole series about 260 removals of the cuticle 

 from usually 10 to 12 points in each apple took place. In about 

 5 or 6 cases the cut was a little below the cuticle. Part of the solu- 

 tions (series A) were prepared by myself, part (series B) liy Dr. 

 Rotheia, Miss Kincaid and Miss Jackson. The apples were placed 

 in the solutions by one of the three foregoing. They were kept in 

 a locked cupboard by Dr. Hall and inspected jointly after 3 and 

 7 days' immersion. The solutions were then poured away, the 

 apples and cylinders washed with distilled water, left for a week 



