PROTEINS 165 



pronounced colloid character. Chemically, it is composed of the 

 protein globin, a histone, and the iron-containing component, hematin, 

 which is apparently a pyrrol derivative. 



BECHHOLD used 1 per cent hemoglobin solutions to gauge his 

 ultrafilters (see p. 99). 



After dialyzing three to four months, hemoglobin solutions have a 

 conductivity of K 20 = 1 X 10~ 4 . After dialyzing five and a half 

 months, the hemoglobin was completely precipitated though the pre- 

 cipitate did not have the amorphous flocculent character of other pro- 

 teins but was more granular although no crystalline formations could 

 be recognized. If the granules were removed by filtration during the 

 dialysis, there was obtained a reddish, optically inactive solution 

 which showed no particles in the ultramicroscope. Such a solution 

 does not pass through the dialyzing membrane and contains particles 

 which are somewhat larger than those of serum albumin as deter- 

 mined by ultrafiltration. 



Regarding the absorption of O and COz by hemoglobin see page 

 308, et seq. 



During dialysis, hemoglobin changes to methemoglobin. Met he- 

 moglobin, which is insoluble in water and neutral salts, redissolves 

 upon the addition of traces of alkalis or acids. 



Purified hemoglobin migrates to the anode. In view of this fact 

 and the relatively high conductivity of a dialyzed hemoglobin solution 

 P. BOTTAZZI assumes that hemoglobin is an hemoglobinic acid in- 

 soluble in water, but which exists in solution as an alkali hemoglo- 

 binate. Being an amphoteric electrolyte it is also soluble in acids and 

 then migrates to the cathode; its H ion dissociation far exceeds its 

 OH ion dissociation. According to L. MICHAELIS, on the contrary, 

 hemoglobin is less acid than serum albumin; its isoelectric point 

 occurs with an H ion concentration of 1,8. 10~ 7 . The viscosity curves 

 which P. BoTAZZi* 1 obtained on dissolving it in alkalis and acids 

 indicate the occurrence of methemoglobin ions; they resemble the 

 viscosity curves of alkali and acid albumin. Completely dialyzed 

 methemoglobin coagulates at 47-53C.; in the presence of traces 

 of alkalis or acids, and in the absence of neutral salts coagulation 

 fails to occur even at 100 C. 



In conclusion we shall mention the mucins and mucoids. They 

 are the excretory products of many glands and may be briefly de- 

 scribed as animal mucus. The possession of a carbohydrate in ad- 

 dition to the protein component distinguishes them chemically. 

 Colloid-chemically they also occupy an intermediate position, since 

 they are not coagulated by heat but are precipitated by salts and 

 alcohol. Because of their acid character they are precipitated by 

 acids and dissolved by alkalis. 



