1893.] Arrow- Poison of the Wa Nyika and other Tribes. 155 



When to the crystals themselves a little strong sulphuric acid is 

 added, a pink colour is 'almost immediately developed, which soon 

 darkens to a brick-red, and then slowly fades to pale brown. Dilute 

 sulphuric acid, with moderate heat, changes the colourless crystals 

 rapidly to brick-red, and then gradually chocolate and green colours 

 are developed. 



The exact melting point is not easily ascertained. When heated to 

 about 184° C, the crystals suddenly almost disappear, and the soft 

 substance remaining undergoes little further change until a tempera- 

 ture of rather over 200° 0. is reached, when the colour becomes 

 brown, and bubbles of gas are liberated. 



~No nitrogen or inorganic matter is present in the crystals. When 

 they are heated at 100° C. in 2 per cent, sulphuric acid, a brownish 

 amorphous substance is deposited, and the neutralised filtrate causes 

 an abundant reduction in Fehling's solution, showing that the active 

 principle is a glucoside. 



Two concordant combustions made for us by Dr. Dobbin, of the 

 Chemical Laboratory of the University, indicate that the probable 

 formula of the substance is C30H52O14. 



These characters show that this active principle closely resembles, 

 if it be not identical with, a crystalline substance separated by 

 Arnaud,* by a more complicated process than the above, from the 

 wood of a plant obtained in the Somali country ; and, although the 

 species has not yet been identified, the plant has, from an examina- 

 tion of the twigs and wood, been placed in the genus Acokanthera.f 



On testing the pharmacological activity of the crystalline active 

 principle obtained by us from the Acohanthera wood, we found that 

 the minimum lethal dose for the frog (Bana temporaria) was between 

 0-00004 and 0*00005 grain per 100 grains of weight of frog. The 

 latter dose always caused death, usually in from three to six hours ; 

 the former dose was not lethal. Rabbits died usually in a little over 

 an hour after the subcutaneous administration of from 0*00003 to 

 0*000035 grain per 100 grains (l/400th to l/500th grain per pound) of 

 weight of rabbit. 



The arrow- poison itself was found to have only one-fourth the 

 lethal power of the crystalline active principle. 



In a series of experiments on frogs and rabbits we found certain 

 effects to occur so uniformly that they may be regarded as character- 

 istic of the action of the poison. 



In the frog the prominent effects which follow the subcutaneous 

 injection of large lethal doses are : — Slowing and intermittence of 

 respiration ; gaping of the mouth, often accompanied with straining 



* ' Comptes Rendus,' vol. 106, 1888, p. 1011, and vol. 107, 1889, p. 1162. 

 f Ibid., vol. 107, 1889, p. 1162, and 'Bulletin G-en. de Therap.,' vol. 117, 1889, 

 p. 107. 



