1920] 



MACDOUGA l—biocolloids 



129 



6. Every measurement obtained by this method is an average 

 of the action of three sections, and has the value of an average. 

 Any value showing notable departures from expectancy should be 

 repeated. 



7. Measurements of the swelling of sections by the auxograph 

 give variations in thickness, and serve as direct indices of total 

 changes in volume in plates of agar and agar mixtures, as this 

 material has a strict tendency to return to its original form. Sec- 

 tions of gelatine swell in all dimensions no matter how the plates 

 are cast. 



It was desirable to use the best known and most available 

 pentosans or hemicelluloses, and agar-agar, acacia gum, tragacanth, 

 mesquite'gum, cherry gum, and mucilage of Opuntia were selected 

 for the tests. According to information furnished by H. Nakano 



* 



of the Botanical Garden of Tokyo, agar is prepared chiefly from 

 the algae Gelidium amansii Lamour, G. pacificum Okam, G. linoides 

 Kiitz., and Pterocladia capillacea Born, et Thur., while some 

 material of Gelidium subcostatum Kiitz., Ceramium Boydenii Gepp., 

 Campylaephora hypenaloides Y. Ag., and Acanthopeltis japonica 

 Okam, etc., may be included. The process includes washing in fresh 

 water, decoloration in the sun, milling, boiling, filtering, maceration 

 in sulphuric or acetic acid, freezing, and drying. Modernized 

 methods simplify this treatment somewhat. Salts, amino-acids, 

 etc., may be present in the final product, and, as it was desirable 

 to reduce the amount of all such subtances, the interest of 

 E. R. Squibb and Sons was obtained, and a purified product was 

 made by the following procedure. 3 



A good grade of commercial agar was dissolved in distilled 



* 



water and jacketed with superheated steam. The viscous solution 

 produced thereby was filtered clear through a thick mass of steam- 

 jacketed paper pulp, under diminished pressure. The clear solu- 

 tion of agar was dialyzed for about 10 days in a steam-jacketed bath 

 containing running distilled water. After removal of diffusible 

 carbohydrates and salts by the dialysis through parchment paper 



3 For further information concerning the origin and preparation of similar products 

 see Swartz, M. D., Nutrition investigations on the lichens, algae, and related sub- 

 stances. Trans. Conn. Acad. Arts and Sci. 16:247-382. 191 1. 







