STRUCTURAL BASIS OF THE HUMAN BODY. 



I. Motion. It is probable that the protoplasm of all cells is capable 

 at some time of exhibiting movement; at any rate this phenomenon, 

 which not long ago was regarded as quite a curiosity, has been recently 

 observed in cells of many different kinds. It maybe readily studied in 

 the Amoebae, in the colorless blood -cells of all vertebrata, in the branched 

 cornea-cells of the frog, in the hairs of the stinging-nettle and Trades- 

 cunt ia. arid the cells of Vallisneria and Chara. 



These motions may be divided into two classes (a) Fluent and (b) 

 Ciliary. 



Another variety the molecular or vibratory has also been classed by 

 some observers as vital, but it seems exceedingly probable that it is 

 nothing more than the well-known "Brownian" molecular movement, a 

 purely mechanical phenomenon which may be observed in any minute 

 particles, e.g., of gamboge, suspended in a fluid of suitable density, such 

 as water. 



Such particles are seen to oscillate rapidly to and fro, and not to pro- 

 gress in any definite direction. 



(a.) Fluent. This movement of protoplasm is rendered perceptible 

 (1) by the motion of the granules, which are nearly always imbedded in 

 it, and (2) by changes in the outline of 

 its mass. 



If part of a hair of Tradescantia 

 (Fig. 1) be viewed under a high magni- 

 fying power, streams of protoplasm con- 

 taining crowds of granules hurrying 

 along, like the foot passengers in a busy 

 street, are seen flowing steadily in defi- 

 nite directions, some coursing round 



the film Which lilies the Ulterior Of the 



,, , 

 Cell-wall, and Others liowmo; toward 



Or 



FIG. 1. Cell of Tfcidescantia drawn at 

 successive intervals of two minutes. The 

 cell-contents consist of a central mass con- 

 nected by many irregular processes to a 

 peripheral film: the whole forms a vacuo- 



. , . - 



from the irregular maSS in the lated mass of protoplasm, which is continu- 

 , , .. ,, ally changing its shape. (Schofield.) 



centre of the cell-cavity. Many of these 



streams of protoplasm run together into larger ones, and are lost in 



the central mass, and thus ceaseless variations of form are produced. 



In the Amoeba, a minute animal consisting of a shapeless and struc- 

 tureless mass of sarcode, an irregular mass of protoplasm is gradually 

 thrust out from the main body and retracted: a second mass is then pro- 

 truded in another direction, and gradually the whole protoplasmic sub- 

 stance is, as it were, drawn into it. The Amoeba thus comes to occupy a 

 new position, and when this is repeated several times we have locomotion 

 in a definite direction, together with a continual change of form. These 

 movements when observed in other cells, such as the colorless blood- 

 corpuscles of higher animals (Fig. 2) are hence termed amoeboid. 



Colorless blood-corpuscles were first observed to migrate, i.e., pass 



