6 PROTOPLASM 



ently abnormally. The most conspicuous and well known 

 among the former are the pseudopodia, or lobelike protrusions 

 put out from the surface of Amoeba (Fig. 24) and like organisms 

 by means of which they move. Similar but much finer are the 

 protoplasmic protrusions from bacteria which may also serve 

 for the purpose of locomotion. Other structures of the same 

 kind have been quite extensively studied under the name of 

 filose threads (of the Foraminifera and Radiolaria). The fact 

 that certain fatlike substances (lipoids) form identical processes 

 (myelin threads) (Fig. 176) has led to the belief that the sur- 

 face of protoplasm is of such a material. Very interesting are 

 the protoplasmic protrusions given off by unripe eggs of Echino- 

 derms when in the presence of sperm (Fig. 175). Sperm arc 

 necessary to arouse the surface protoplasm into such activity. 

 The structures are without evident function. Similar processes 

 formed by the ripe egg awaiting fertilization may serve a purpose, 

 to guide the sperm. All such activities indicate that the surface 

 of protoplasm can be as active as is the inner protoplasm. 



Studies on protoplasm may be chemical or physical. The 

 physical properties of protoplasm are the subject of most of the 

 chapters which follow. Certain properties have been ascer- 

 tained which are as yet of purely theoretical interest; such are 

 specific gravity determinations. Pfeiffer obtained values of 

 these varying from 1.025 to 1.06, with 1.04 as an average. 



Chemically, protoplasm is three-fourths water. Of the remain- 

 ing solid matter, the greater part is protein, the rest being mostly 

 carbohydrates (sugars), fats, and salts. The maximum water 

 content of protoplasm cannot be stated with certainty; where it 

 appears to be very great, as in the jellyfish, one cannot say how 

 much of the organism is really protoplasm and how much just 

 nonliving jelly. Gortner states that the jellyfish is a living 

 system in which water plays a role probably more important 

 than that of any other single constituent. The maximum water 

 content of the jellyfish is given as 99.8 per cent; therefore, only 

 0.2 per cent is dry matter. The water content of tadpoles may 

 be nearly as high. In man, the amount of total water is about 

 65 per cent, lowered to 53 per cent by old age or disease. A 

 probable minimum water content of protoplasm is 8 per cent in 

 dormant seeds. These may live for more than a hundred years. 

 (Two hundred years for seeds of Nelumbo, the Japanese water 



