4 i4 SCIENCE PROGRESS 



The oblique incisions yield the latex, and the vertical groove 

 serves as a channel of conduction to the basal receptacle. At 

 each subsequent tapping a thin paring is taken off the lower 

 edge of each oblique cut ; the vertical groove is left untouched. 

 Thus the extraction of latex from the area of trunk covered 

 by the herring-bone can be continued, till the whole of the 

 bark intervening between the original slanting incisions has 

 been excised. 



The half herring-bone is now generally preferred, as 

 being less severe than the full herring-bone. A quarter of 

 the girth of the trunk can be tapped on the former system 

 each year. By the time (four years) the whole has been 

 so treated, the renewed bark on the first area will be 

 sufficiently mature to allow the multiple tapping to be 

 recommenced. 



Two important points should be observed in modern tapping. 

 The wound should be reopened by as thin a paring as possible ; 

 and every care should be taken not to injure the cambium. 

 The longer the bark can be made to last, the greater, as a rule, 

 will be the yield of rubber. Shavings of bark one-twentieth of 

 an inch or even less in thickness are now managed in practice. 

 A foot of bark can, therefore, be made to last for about 250 

 successive tappings. 



A wound which passes through the cambium into the wood 

 heals badly. In the excision method of tapping careless mani- 

 pulation results in an uneven bark renewal, producing a surface 

 difficult to tap in a systematic manner. Consequently to guard 

 against cambial injury and to ensure thin parings much ingenuity 

 has been exercised in devising suitable tapping instruments. 

 At least two dozen different knives have already been invented 

 for the purpose. 1 Some of these have met with favour and are 

 commonly used. 



Pricking. — Since economy in bark excision is so important, 

 the idea that puncturing might be substituted to some extent for 

 paring was early mooted. A tool, termed the pricker, was 

 brought out for the purpose. Good yields were obtained by 

 the combined use of the parer and pricker. The bark was thus 

 made to last longer. 



1 For details the reader is referred to Wright's textbook, pp. 79-88 (Hevea 

 brasiliensis or Para Rubber, 3rd edit. 1908) and to the pages of the India- Rubber 

 Journal for the latest knives. 



