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BEPOET OF CHEMICAL LABOEATOEY 



••Tapping" 

 experiments 



explain the results which were obtained from the attempted inoculations of hashnh 

 trees in 1907.' The experiments made at that time were as follows : — Tapping was 

 performed by making a series of gashes with an axe, no bark being stripped off, and 

 (as it was thought that the chances of efficient inoculation might thus be lessened) an 

 attempt was made to ensure the entrance of the microbe by rubbing a moist rag over 

 the bark, in which the microbe was presumed to reside, and subsequently into the cut. 

 A series of trees tapped in the usual native fashion, by stripping the bark, were 

 also treated in the same manner for comparison. The number of trees operated on in 

 each case was twenty-five. The following table exhibits tlie results obtained : — 



Methods of 

 tapping 



When the results were reported it was suggested that possibly the lower yields 

 were due to the fact that in place of increasing the extent of infection, the procedure 

 adopted had, on the contrary, lessened it, since the sajj exuded was, in great part, 

 removed by the wet cloth. If we accept the view that ants are the chief carriers of 

 infection the results become still more comprehensible. A portion of the sap having 

 been removed (and the amount exuded is usually very small) there was no longer 

 sufficient present to attract the insects, in the usual number, before the cut had healed. 



Another point which is of interest in this connection is the effect of cold at the 

 time of tapping. No further experiments have been made since those already reported 

 on, but these appear to show conclusively that cold at the time of tapping has a 

 marked retarding effect on gum production. Should the weather remain cold for several 

 successive days after tapping, the operation may even be entirely fruitless. It seems 

 reasonable to conclude from this that the growth of the microbe is inhibited by the low 

 temperature, and that the wound heals before the tree has become suflBciently infected. 



It should be stated here that the exact determination of the quantitative effect of 

 any given condition on gum production is far from easy by reason of the difficulty in 

 securing a reliable standard for comparison, /. e. a tree of the same age and size, 

 perfectly sound, to the sap of which the microbes are unable to gain access. Small 

 cracks or fissures at one point or another are almost sure to be found during the dry 

 season, and a certain indeterminate amount of infection appears to be inevitable. 



Methods of tapping. The native method of tapping hash/ib trees is to remove a 

 strip of the bark, from 2 to 3 feet in length and 1 to 3 inches broad, according to the 

 size of the branch operated upon. Trials have been made to improve upon this method 

 by removing shorter strips, or by simply gashing the tree, but up to the present, the 

 native method appears to yield the best results. 



Tapping of gum trees is only a comparatively recent practice in Kordofan, and is 

 said to date from about 30 years ago. Previous to this, only such gum was collected 

 as was found exuding from natural fissures in the bark. Tapping by the present 

 method was found to increase the yield to something like five times the former amount. 



Fide Third Report, Wellcome Tropical Research Laboratories, p. 422 



