PRELIMINARY NOTES ON THE CHEMISTRY OF THE LATEX 01' CALOTROl'IS TROCERA 89 



The possibility that plant juices, other than those of 0. procera, may give a similar 

 reaction, has not been overlooked, and special attention has been devoted to the 

 examination of foodstuffs in common use among the natives, and which might, therefore, Examination 

 be present in the stomach contents of suspected cases. The test has been applied to "' ("othiuns 



. ^ ^"^ to exclude 



between twenty and thirty varieties of dura, which is the staple food in the Sudan, and to possibility 

 as many common vegetables and fruits. The foodstuffs were crushed, macerated for °^ <:onhision 

 several hours in 0-2 per cent, hydrochloric acid, and the reagent added to the strained and 

 filtered liquids. The pale-coloured varieties of dura gave no ring or coloration on 

 shaking. In the case of the red varieties, however, a pink ring was developed, and a deep 

 crimson solution obtained on shaking. A strong extract of a red variety of dura, to 

 which a small amount of latex liad been added, gave with the reagent a purple coloration, 

 as was to be expected. Further examination of the dura extract showed that the 

 red colouring matter is entirely removed by basic lead acetate when added to a faintly 

 acid solution. Since the colourable substance of the latex is not so precipitated, the 

 presence of red dura in no way interferes with the test, as several trials on red dura 

 extracts to which small quantities of latex had been added, have proved. 



Of the other foodstuffs examined, none was found to give the deep Prussian l)lue 

 colour produced by the latex. The majority gave pale yellow or greenish-yellow rings, 

 and pale yellow colorations on shaking. Two, the cucuiuber and sweet potato (Arabic, 

 hamhe) give pale blue rings, and pale blue colorations. The pumpkin (Arabic, yara) 

 gives a purplish-blue colour, and the vegetable marrow a yellowish-green. TJiis latter 

 colour was found to mask the colour given by the latex when the reagent was added to a 

 mixture of a very small quantity of latex and a large quantity of vegetable marrow, a 

 green tint being imparted to the bhie. With the latex in larger proportion, the green 

 tint was not seen. 



The foodstuff extracts were also treated with lead acetate, etc., as previously 

 described (vide jpar/e 88), and the reagent applied to tlie decomposed ammoniacal basic lead 

 acetate precipitates. Some differences in the colour reactions given were observed. The 

 cucumber gave a pale blue colour, which changed slowly to pale pink, and the pale blue 

 colour given by the sweet potato was rapidly discharged. The vegetable marrow gave 

 no ring or immediate coloration, but a strawberry-pink colour developed on standing. 

 The pumpkin gave a pale heliotrope colour, becoming more pronounced, and then fading. 

 In all cases the colour faded comparatively quickly ; a solution of latex similarly treated 

 gives a Prussian blue colour, which does not fade until after some considerable time. 

 In carrying out these tests the liquids were not cooled after shaking, and the fading of the 

 colours in the case of the vegetables may be due to the heat developed. It is worthy of 

 note, however, that the blue colour of the latex does not readily fade under these conditions. 



It is to be borne in mind that the degree of dilution of tlie latex, wlieu no intei'fcring Effects of 

 body is present, determines whether the blue coloration can be correctly described as '•''"""" °" ''"" 



•< ^ ' Prussian lilue 



Prussian blue. Dilutions of 1 in 5 to 1 in 25 give an unmistakable Prussian blue, 1 in 50 coloration 

 gives a pale Prussian blue, while 1 in 250 gives what could \h'. described as a pale blue, 

 although of exactly the same tint as a much diluted solution of Prussian blue. 



The depth, purity and permanence of the blue colour given by the latex aie quite 

 distinctive, but a confirmatory reaction has been discovered which eliminates any risk of 

 mistaking these foodstuff colours for tlie colour of the latex, and also enaljles tlu^ latex 

 to be detected with certainty when mixed witli tliese foodstuffs. 



A very striking colour-reaction, which, so far as is at present known, is characteristic 

 of the latex, is given by sulphuric acid containing a trace of formaldcliydc. The reagent 



