The Cell 21 



them very much like legs ; according to another theory, by a process which 

 may be described briefly (if not quite accurately), as " putting out a pseu- 

 dopodium and then crawling into it." Cells which creep about in this way 

 are called wandering cells, of which there are several sorts in the human 

 body, among them the white blood corpuscles, or leucocytes [Fig. 3], and 

 the osteoblasts [Fig. 15]. From the amoeba [Fig. 7], a typical unicellular 

 animal found in pond-water, this method of locomotion is called amoeboid 

 movement. 



By means of pseudopodic projections of its cytoplasm a wandering cell 

 may surround foreign particles, which if nutritive, may be assimilated 

 within the cell, or if not, may be carried to another place and there de- 

 posited. 



The activity of every living cell, and therefore of every living organ- 

 ism, is regarded as based chemically on the processes of assimilation and 

 dissimilation. Assimilation is the conversion of food materials into new 

 protoplasm ; dissimilation is the breaking-down of protoplasm into waste 

 products, and is usually accompanied by, or consists in part in, oxidization. 

 Certain cells are able to carry on, in addition to assimilation proper, the 

 synthesis of non-living substances to be stored up in the cell, such as fat,, 

 sugar, and starch, or to be cast out, as glandular secretion. Such syn- 

 thesis, and assimilation likewise, is accompanied by the transformation of 

 kinetic energy received from without (as from the sun's rays in the case 

 of plants producing starch), or from dissimilation within the cell, into 

 potential energy. Dissimilation liberates energy, which may be utilized in 

 anabolic processes, or may be available as heat to maintain the temperature 

 of the organism, or may be expended in work, as in the contraction of 

 muscle or the conduction of a stimulation in a nerve cell. 



REFERENCES ON THE CELL. 



Luciani, Human Physiology, (Translated by Welby), Vol. I, Chapters I, II, III. 



Wilson, The Cell in Development and Inheritance. Chapters I, II. 



Schafer, Microscopic Anatomy (Vol. II, Pt. I, of Quain's Anatomy, Eleventh 



Edition), § Structure of the Tissues, Sub-§ The Animal Cell. 

 Bailey, Text-Book of Histology, 3d Edition. Pt. II. Chapter I. 

 Lewis and Stohr, A Text-Book of Histology, Pt. I. Chapter I. 

 Starling, Human Physiology, Pt. I., Chapter II. 



Sedgwick and Wilson, Introduction to General Biology. Chapters I-III. 

 Hertwig, Manual of Zoology, (Translated by Kingsley), General Anatomy, I. 



