HEART-ROT 89 



is hard, but readily becomes soft on the addition of water, 

 though the solution is not adhesive. 



The gummy nature of this substance, its solubility in 

 water and insolubility in alcohol, showed it to be either 

 a gum or a dextrin. On hydrolysing for half an hour by 

 boiling with dilute H 2 S0 4 , it gave large quantities of sugar 

 which was capable of reducing Fehling's solution. This 

 led me to suppose that the substance was a dextrin, but 

 Dr. D. H. Vernon kindly tested it for me and identified it 

 as a gum. The distinction was based on the readiness with 

 which an aqueous solution is precipitated by alcohol, and 

 on the detection of pentose sugars as a result of its hydro- 

 lysis. If alcohol to 51 per cent, be added to a 20 per cent, 

 solution of the gum, a dark-brown gummy mass is thrown 

 down and a moderate amount of white precipitate is retained 

 in solution. If alcohol is added to the filtrate up tc 64 per 

 cent., a considerable further white precipitate is thrown 

 down, while alcohol to 70 per cent, brings down a very 

 copious white precipitate. No further precipitate results 

 from adding more alcohol, so that we may conclude that 

 an excess of alcohol to 70 per cent, precipitates all the gum. 

 Dextrins, on the other hand, do not begin to be precipitated 

 till the alcohol exceeds 70 per cent. If the solution be 

 kept for some time the presence of pentose sugars may be 

 detected by the phloroglucol and orsinol tests, which give 

 very marked results. And since the gum was derived by 

 precipitation by alcohol from a watery extract of the wood, 

 it cannot be maintained that the pentose sugars were present 

 from the first, as such impurities would not be precipitated 

 by the alcohol. 



Now it is known that in the process of delignification 

 a number of pentose derivatives are removed from the cell 

 walls, and we may here seek the source of the gum found 

 in the early stages of rot. Very little is at present known 

 about the chemical constitution of gums, and the term is 

 applied rather vaguely by biochemists ; but as far as I know 

 this is the first occasion in which a member of this class of 

 substance has been isolated from a conifer. In the trunks 



