Fundamental Features of Phytocolloids. 15 



phase, and the protein the internal discontinuous or globular phase. 

 This conception is a very attractive one because of the possibilities 

 implied. Included among these would be the play of osmotic forces 

 in the inclosed and non-diffusible gelatine, which might be a contribu- 

 tory factor in the high swelling coefficients displayed by biocoUoids.^ , 



The sections and plates of agar and proteins, amino-acids, etc., used 

 in the accompanying experiments probably included the materials in 

 many possible arrangements, but as the method of preparation was 

 uniform, the relative value of the results obtained from them remains 

 unimpaired. This heterogeneity is a direct resultant of the varying 

 history and unequal disposition of the material which enters into the 

 colloidal mass, and would find direct parallel in living matter, which is 

 practically never homogeneous as to composition or uniform as to 

 architecture throughout any measurable mass, and hence its morpho- 

 logical units are not isotropic as to action when measured with com- 

 mensurate accuracy. 



The experimenter dealing with the hydration of these elastic gels 

 does not proceed far before he becomes aware that the method of com- 

 pounding, melting, drying, temperature, and other features of the 

 experience of the biocoUoids influence the behavior of the thin plates 

 w;hich may be made from them. It will be important, therefore, to 

 describe the preparation of the sections which were used in these and 

 other tests. 



The agar and the proteinaceous material should all be from one 

 source and if possible from a single lot in any comprehensive series of 

 tests where close comparisons are desirable, as it can by no means 

 be assumed the composition of separate lots will be identical as to 

 salt or nitrogen content. The variations in gelatine are not so easily 

 apprehended. Both agar and gelatine, or other proteinaceous com- 

 pound used, should be first soaked in distilled water at some tempera- 

 ture between 15° and 20° C. for a period of a half hour. The agar is 

 now heated with an amount of distilled water over a water-bath that 

 will bring it to a 2.5 per cent solution or suspension. The suspension 

 of the agar may be accomplished more quickly by the use of an auto- 

 clave. When this is completed, and it is difficult to bring the last 

 particles into liquid form, it should be filtered hot into a flask to obtain 

 a clear solution. If the biocoUoid is to be made by the addition of an 

 amino-acid, any one of these substances may be added at temperatures 

 between 50° and 80° C, but when albumins are used the agar solution 

 must be cooled in a warm water-bath until it comes down to a tempera- 

 ture below the coagulation-point of the latter substances. This will 

 be found somewhere below 40° C, and the protein solution should be 

 poured in with sufficient stirring to procure good admixture, or the 

 same end reached by a vigorous shaking. 



1 See discussion in Robertson, T. B., The physical chemistry of proteins, pp. 294-350. New 

 York and London. 1918. 



