CAREY: GROSS STRUCTURE OF AN AGAR GEL Wi 
below 7.5 per cent, has Somewhat the appearance of branching; 
the cavities being shaped in section like a biconvex lens. In the 
10, 8, and 7.5 per cent gels there were fewer large cavities and more 
fine pores or slits (Fic. 4). In the weaker gels larger slits and 
fewer finer ones are seen (FIGS. 1-3). 
The figures show a gradual change from the coarser to the 
finer structure as the per cent of agar in the gel increases. It 
seems as though this change 
probably commenced between 
the 5 and the 7.5 per cent gels 
though this has not been defi- . | { | 
nitely determined. Narrower 
gels are dried at high tempera: 
tures, i.e., more rapidly. Strips 
not dried on the frames showed ‘| h 
structure, but curled somewhat ; 
‘in drying. The 2.5, 3 and 5 per | 
cent gels after soaking in water 
could be peeled off in layers. | i \! 
It seems possible that the : 4 
structure of the gels, which when : ( 
\ ( 
| 
— 
- 
. 
. first set must be isotropic, be- " 
comes anisotropic on drying due 
to the strains set up within the 
mass. It would seem to the } 
writer that the long axis of the | 
particles, after drying, would be 
in the horizontal plane of the | 
gel. This might cause splits in 
it in the horizontal and not in Fic-1. Ao.5 percent napecoetenl ge 
the vertical plane, as the water en rer ee 
is withdrawn, as is the case here. This is, however, only a sug- 
gestion as the gels were not examined with a polariscope. 
Ambronn* found that thin layers of agar and gelatine, when 
frozen and dried on glass plates, gave the appearance under the 
microscope of a fine network which, he says, looked almost like a 
* Ber. Verhandl. Kénigl. Sachs. Ges. Wissens. Math. Phys. K1. 1891: 28-31. 
