58 Hydration and Growth. 



used for solution a swelling in excess of the expectancy resulted. It 

 was also seen that the surface of the liquid became covered with thin 

 crystals. In all probability the solution or dispersion of some agar 

 into the water resulted in the displacement of some of the acid, with 

 the result that the sections were actually hydrated from a solution less 

 concentrated, giving a swelling in excess of the expectancy. 



Tests were now made at the same temperature and under the same 

 conditions with plates consisting of agar (8 parts) and gelatine (2 

 parts), in order to ascertain the results when the carbohydrate was in 

 colloidal combination with complex amino-compounds. The trios of 

 sections had shown swellings of about 1,700 per cent in distilled water 

 under the same conditions and had an average thickness of 0.28 mm. 



TABLE 46. 



p. ct. 



Aspartic acid, 0.05 M 910 



Aspartic acid, 0.0002 M 1 , 090 



Aspartic acid, 0.00008 M 1,786 



The effect of the acid is seen to vanish at a much greater concen- 

 tration than on the agar alone, the swelling at saturation being about 

 half that of distilled water. 



After the experience noted above, new plates of agar (9 parts) and 

 aspartic acid (1 part) were made. The amino-acid was placed in the 

 water in which the agar was liquefied to a 2.5 per cent solution. The 

 usual translucency of the agar was modified to a pale milky appear- 

 ance, and its viscosity seemed to be decreased. Soon after setting, 

 cracks and fractures appeared in the plates. This of course allowed 

 shrinkage in the long axes of the plates and would make it impossible 

 for the sections to swell in thickness to the same proportion as the 

 coherent agar plates. These new plates came down to a thickness of 

 about 0.16 mm. and showed swellings of 220 per cent in distilled water 

 at 16 C. and of a slightly greater expansion in a solution of 0.05 M 

 asparagin, in which the swelling was 281 per cent. It is to be noted 

 that while the aspartic acid is present in a more concentrated condition 

 in these plates than is possible in water, yet the entire amount was 

 held in the colloidal mesh or plate and showed no formation of crystals 

 on the surface or in the sections, as in the case of the less-soluble tyrosin. 

 The hydration of the colloid with the acid incorporated in it is less 

 than that which may take place when the acid is dissolved to saturation 

 in the water in which the swellings are made. The influence of this 

 acid on agar was not widely different from that of succinic acid, but it 

 caused greater swelling in equimolecular concentrations hi gelatine, 

 agar-gelatine, and agar-protein. 



The amine of this group was now tested both in solution and in- 

 corporated in agar sections. Plates of agar (9 parts) and asparagine 

 (1 part) were prepared and swelled in comparison with aspartic acid, 

 giving results shown in table 47. 



