the harder the sponge. The greater number of 

 simple branching of the fibers, the softer and 

 more absorbent the sponge. 



2. The sponges with connecting fibers of 

 about .02 mm. thickness appear to be the most 

 elastic. The thicker the fiber, the more rigid 

 the sponge. Finer the fibers, softer the sponge. 



3. If any of the fibers of the sponge con- 

 tain foreign bodies, these fibers are readily 

 crushed when the sponge is compressed and the 

 sponge loses its elasticity. 



4. The more numerous the fibers per unit 

 of volume, the greater the capillary action 

 and the more water the sponge can hold. 



The above fiber characteristics are of 

 interest because of the differences between 

 the fiber structure of the main commercial 

 species of sponges and the differences between 

 the fiber structure of wool sponges growing in 

 different ecological conditions. The series of 

 photomicrographs in figure 2 illustrate the 

 variations. 



In the wool sponge fibers, figure 2a, the 

 individual fibers are very fine, about .02 mm. 

 in diameter. By comparison with other sponges 

 the meshes are much smaller; this property 

 gives the wool sponge the ability to hold much 

 larger quantities of water than any other 

 sponge and also makes it softer to the touch. 

 All fibers are much the same size, and in the 

 area of the conules, as shown in the photograph, 

 the fibers tend to be clumped together, giving 

 greater support at the sponge's surface. 



Two distinct kinds of fibers are found in the 

 yellow sponge and all others of the genus 

 Spongia. The ascending or principal fibers are 

 normally oriented perpendicular to the sponge 

 surface. These usually contain bits of fine 

 sand or spicule particles from other sponges 

 as inclusions within the fibers (fig. 2b). The 

 mesh, or secondary, fibers may be two or 

 three times as thick as the thickest fibers of 

 the wool sponge. The meshwork also con- 

 tains more interconnections than that of the 

 wool sponge. 



The looser meshwork of the yellow sponge 

 does not make it possible for this sponge to 



hold as much water as the wool and allows the 

 sponge to be torn more easily. With the heavy 

 fibers perpendicular to the surface, the sponge 

 is torn into segments under any hard usage. 



In figure 2c of the grass sponge fibers, the 

 coarseness of the individual fibers and the 

 fairly regular pattern make this sponge feel 

 hard. The large size of the meshes prevents 

 this sponge from holding much water. 



The arrangement of the fibers of the glove 

 sponge, figure 2d, is much the same as the 

 yellow sponge although the meshwork is finer. 

 Unfortunately the entire sponge is arranged in 

 narrow perpendicular columns (fig. 1) with 

 deep clefts between so that the sponge is very 

 weak and easily torn into sections. 



The fiber arrangement of the wire sponge, 

 figure 2e, is latticelike, the meshes very 

 regular and entire in shape. This arrangement 

 combined with the large mesh size makes the 

 sponge incapable of holding water and renders 

 it almost valueless commercially; however, it 

 would serve as good insulating material. 



The fibers of the finger sponge, figure 2f, 

 are arranged very differently than those of the 

 other sponges. The core is made up of a regular 

 meshwork of fibers arranged in line with the 

 branch. In the outer part the fibers are per- 

 pendicular to the branch and are fairly loosely 

 grouped. 



Sponge Grading 



The desirable commercial qualities pos- 

 sessed by a sponge such as softness, fineness, 

 absorptiveness, toughness, elasticity, and dur- 

 ability depend on: (1) the species of sponge and 

 (2) the type of physical environment in which 

 the sponge grows. Considerable skill (and 

 honesty) is attributed to sponge graders who 

 separate the wool sponges into a number of 

 grades. Other species of sponges are not 

 usually graded at present because of the small 

 take. The method of grading has at times been 

 very complex. 



Sponge grade is determined by texture, 

 shape, and solidity. 



