On the gross structure of an agar gel 
CorNELIA LEE CAREY 
(WITH FOUR TEXT FIGURES) 
In connection with some other work on the behavior of agar 
gels a peculiar appearance was noticed in certain dried strips of 
agar which had been swollen in water. In these cases the swollen 
gels, when removed from the water, would exude a considerable 
amount of the adsorbed liquid under slight pressure. This led 
to an examination under the microscope, where it was found that 
the gel had a decided lamellated structure. Later it was noticed 
that these lamellations were visible to the naked eye and could 
be seen when light was reflected upon the cut surface. It seemed - 
of interest to investigate some of the causes influencing the 
formation of this structure, and the relation its appearance might 
bear to the concentration of the gel. 
A brief notice of this phenomenon has already been published 
in D. T. MacDougal’s recent contribution on hydration and 
growth* from data supplied by the writer. 
The method of preparing the agar was that used by Mac- 
Dougal and described by him in this paper, except that silk was 
used to cast the agar upon instead of filter paper, as the former 
could be more easily removed from the agar than the latter. 
Prepared in this way, the gels were at first allowed to stand over 
night in the room, and then dried at a temperature of about 
70° C. It was found, however, that this first slower drying in the 
room had no effect on the structure, as gels put immediately into 
the dryer as soon as set had the same appearance. It is, of 
course, to be understood that the lamellations did not appear 
until the dried gel had been again swollen in water. 
In order to ascertain whether the tension due to the drying on 
the silk had anything to do with the structure of the gel, a 2.5 
per cent gel was cast as usual, but instead of being stretched on a 
frame it was cut. into strips as soon as set. Some of these were 
* Hydration and growth. Carnegie Inst. Washington Pub. No. 297, 1920. 
: 173 
