1886.] 



Proteid Substances in Latex, 



31 



xanthoproteic reaction, the orange colour on the addition of the 

 ammonia being very marked. On warming the liquid gradually to 

 boiling point there was no coagulation or opalescence, and on adding 

 nitric acid there was no precipitate. Hence the body does not belong 

 to the groups of albumins or globulins. On dropping the boiled 

 liquid into large excess of alcohol, a precipitate was slowly formed, 

 which after standing some hours settled to the bottom of the vessel. 

 These reactions suggested a member of the class of peptones, and as 

 these proteids, though thrown down from their watery solutions by 

 alcohol, are not changed by contact with the spirit, the precipitate 

 was allowed to remain as it settled for about three weeks. At the 

 expiration of that time the alcohol was decanted off, and the precipi- 

 tate dried. It was then found to be freely soluble in distilled water, 

 and to give, as the original latex did, a well-marked xanthoproteic 

 reaction. 



A further resemblance between this body and the group of peptones 

 was revealed by its behaviour when submitted to dialysis. A quantity 

 of the solution of the precipitate that had been standing under alcohol 

 was put into a dialyser and suspended in twice its volume of distilled 

 water. After two days the fluid outside the dialyser was examined. 

 It gave readily the xanthoproteic reaction, and on addition of a large 

 volume of alcohol a marked opalescence appeared, which on standing- 

 became a precipitate. Hence this proteid body appeared to have 

 considerable resemblance to the group of peptones, if not to be a 

 member of it. 



Further examination, however, brought to light some points that 

 indicated a relation to the albumoses also. Saturation of the solution 

 of the alcohol precipitate by solid MgS0 4 gave a copious precipitate, 

 which was redissolved on adding water. The liquid outside the 

 dialyser in the last experiment behaved similarly. The precipitation 

 took place with equal readiness whether the reaction of the solution 

 were neutral or slightly either alkaline or acid. Till recently the 

 precipitation of a proteid by saturation of its solution with a neutral 

 salt was held to be a mark of a globulin, but this reaction cannot now 

 be held to be sufficient of itself to prove this. Halliburton has shown* 

 that it is possible to precipitate serum albumin by such a process, the 

 salt necessary being the double sulphate of magnesium and sodium. 

 Heynsius has statedf that peptone itself may be thrown down from 

 its solution by ammonium sulphate in similar quantity ; a statement 

 that is endorsed by Martin. { Pollitzer§ denies this, as far as true 



* " Journal of Physiology," vol. t, No. 3, p. 182. 

 t " Pfluger's Archiv," Bd. 34, s. 330. 

 X Loc. cit., p. 343. 



§ "Ueber den Nahrwertli einiger Yerdanungsproducte des Eiweisses," "Pfluger's 

 Archiv," Bd. xxxvii, H. 5 & 6, 1885. 



