i REACTIONS OF ALBUMINOUS SUBSTANCES 11 



glucosamin, or an acetyl derivative of the still unknown pentosamin. 

 Friedrich Miiller confirms Ehrlich's statement that pure mucin and 

 mucoid substances do not give the red reaction, if their watery solu- 

 tions are treated directly with the reagent, or even after long treat- 

 ment with boiling mineral acids. Positive results are, however, always 

 obtained if the mucinoid substances are first rendered alkaline with a 

 little alkali or baryta, and if they are then warmed. On adding to 

 these alkaline solutions 2 to 5 per cent solutions of ^-dimethyl-amino- 

 benzaldehyde dissolved in normal hydrochloric acid till the reaction 

 has become acid, a red colour is obtained, especially on heating. 

 Ehrlich showed, microscopically, that in a section of cartilage the 

 perichondrium stains an intense reddish violet, while the hyaline 

 cartilage and the surrounding connective tissue or fat remain colourless, 

 with the exception of a few peri-vascular strands containing elastic 

 fibres, and Mann 1 demonstrated the distribution of the glucosamin 

 histologically by fixing tissues in 0'5 per cent KOH in 90 per cent 

 methyl-alcohol for 24 to 48 hours, or longer at 30 to 40, and then 

 transferring the tissues to a 2 '5 per cent solution of j?-dimethyl-amino 

 benzaldehyde in 1 per cent HC1. 



0. Neubauer believes Ehrlich's benzaldehyde reaction to depend on 

 ' urobilinogen,' but also to be obtainable with albuminous substances 

 in the presence of stronger acids. 2 His pupil liohde 3 confirms the 

 observation of Ehrlich that the benzaldehyde is linked up to proteids 

 by its aldehydic radical, for in addition to the observation of Ehrlich, 

 that formaldehyde, when added to urine, prevents the formation of the 

 red colour, Rohde found the addition of form- and acet-aldehyde to 

 casein to prevent the latter from giving colour-reactions with * Ehrlich's 

 benzaldehyde.' Ehode also showed that the aldehydes of the aliphatic 

 series (form-, acet-, propyl-, butyl -aldehyde) do not give colour 

 reactions ; citral and furf urol give yellow colours, while all aromatic 

 aldehydes show either a red colour (para-dimethyl-amino benzaldehyde, 

 vanillin, salicylic, and cinnamic aldehydes, hadromal) or a green colour 

 (para-nitrobenzaldehyde, amino-benzaldehyde), or a blue colour (genti- 

 sinaldehyde). The only brilliant colours are obtained with 



CHO CHO CHO 



oca 



\-/i 



o 



L 3 



N0 2 OH N(CH 3 ) 2 



p-nitro-benzaldehyde vanillin p-dimethyl-amino-benzaldehyde. 



' l Gustav Mann, Physiological Histology, 1902, p. 299. 



Neubauer, Sitzber. d. Gesell. f. MorphoL u. Physiol. in Mtinchen, 1903, p, 32. 

 ^ 3 Erwin Rohde, Zeit. f. physiol. Ckem. 44. 161 (1905), 



