2 SPONGE SPICULES IX SWAMP SOILS. 



the soil. A thorough examination of the soil, however, made it 

 appear improbable that any of these was the true explanation. A 

 physical action suggested as causing the burning sensation was that 

 the dry, powdered soil, consisting of a mixture of organic matter 

 and the finest of mineral clay particles, produced a drying effect on 

 the skin. The moisture was absorbed so rapidly that an apparent 

 burning resulted. This explanation, however, was not entirely sat- 

 isfactory, and a careful microscopic examination of the soil was 

 made. 



The microscopic examination 1 revealed in the soil the presence of 

 immense numbers of sharply pointed crescent-shaped bodies of 

 siliceous material. These have been identified 2 as siliceous residues 

 (spicules) of certain species of sponge. They are somewhat crescent 

 shaped, about 0.2 mm. long and 0.02 mm. in width and are readily 



FIG. 1. Sponge spicules magnified about 200 times. 



distinguished from the siliceous remains of certain elongated diatoms 

 by the lack of the elaborate sculpturing generally present in the 

 latter. These are the remains of fresh-water sponges and may vary 

 in size and shape. The most common in the Georgia soil is the 

 Mayenia millsii, which is crescent shaped, with tiny spines project- 

 ing from the body of the spicules. The presence of these spicules 

 in large quantities in the soil causes the irritation described. The 

 character of the spicules is shown in figure 1. 



Mayenia millsii is described by Edward Potts 3 as follows : 



Skeleton spicules nearly straight, cylindrical, slender, rather abruptly pointed, 

 entirely microspined. Spines few, low, conical. Measurement of skeleton spicules 

 0.0107 by 0.0005 inch. Collected from Sherwood Lake, near De Land, Fla. 



All the forms of fresh-water sponges as yet discovered are siliceous. The skeleton 

 or framework (corresponding to the elastic fiber of which commercial sponges are com- 

 posed), upon which slimelike sponge flesh, known as "sarcode," is supported, and 



i Mr. W. J. McCaughy made the microscopic examination which located the trouble. 

 * The identification was made by Dr. Albert Mann, Bureau of Plant Industry, who was also kind enough 

 to make examinations of several samples of soil. 

 Synopsis of forms of fresh-water sponges, Philadelphia Acad. of Nat. Scl, 89, 225 (1887). 



