178 THE STRUCTURE OF PROTOPLASM. 



From this it is clear that the pseudopodial protoplasm, that namely to which the more 

 obvious activity of the cell is immediately due, is structureless, and, probably, composed 

 of hyaloplasm alone. The amoeboid movements are produced by a flowing of this hyalo- 

 plasm, which may extend, as in many Ehizopods, far beyond the limits of the spongioplasm. 

 But if the corpuscle is subjected to artificial stimulation of any kind (electrical, mechanical, 

 thermal) the pseudopodia are withdrawn into the body of the corpuscle, which then becomes 

 spherical and appears wholly reticular. The spherical form of the corpuscle represents, there- 

 fore, the completely contracted condition ; it is only in the absence of any obvious source of 

 excitation that the cell throws out pseudopodia. Since the spherical condition is produced by 

 mechanical stimuli, it is probable that the impacts which the white blood-corpuscles are con- 

 stantly receiving in the circulating blood maintain them in the spherical form which they 

 always exhibit within the vessels, and immediately the blood is drawn. It may also be that 

 the inception of foreign particles by amoeboid cells is produced by the excitation which their 

 contact produces upon the portion of hyaloplasm to which they adhere, causing its contrac- 

 tion and withdrawal into the spongioplasm. 



To sum up : The protoplasm of an amoeboid cell is composed of two substances 

 spongioplasm and hyaloplasm. The spongioplasm has a reticular appearance and 

 sponge-like structure, an affinity for staining fluids, is firmer and more refractile 

 than the hyaloplasm, and is probably highly extensile and elastic, but not actively 

 contractile. 1 The hyaloplasm, on the other hand, appears structureless, has little or no 

 affinity for stains, and is highly labile and fluent. It is the active flowing movements 

 of the hyaloplasm which produce the well-known phenomena of amoeboid activity. 

 The spongioplasm forms a sort of framework which serves to support the hyaloplasm, 

 and into which, under the influence of stimuli, the hyaloplasm may become entirely 

 withdrawn. In non-amoeboid cells the hyaloplasm does not extend beyond the limits 

 of the spongioplasm. The latter is the " oecoid," hyaloplasm the "zooid," to adopt 

 terms which Bruecke has introduced into histology, although with a somewhat 

 diiferent signification (see p. 242). 



The question has been frequently discussed whether we are to regard the spherical condi- 

 tion as that of rest, and the amoeboid condition as that of activity, or vice versa. Viewed 

 by the light of the above statements it is clear that both are manifestations of activity, both 

 being produced by flowing of hyaloplasm. In the one case this flows into the pores of the 

 spongioplasm ; this is the condition which corresponds to the contraction of muscle ; in the 

 other case the hyaloplasm flows out of the spongioplasm, producing a condition corresponding 

 to the extension of muscle after contraction. 2 



Whether one or other of the two substances is ever wholly absent from the protoplasm of 

 cells is a question which cannot at present be decided. There are cells and unicellular 

 organisms, both animal and vegetable, in which no reticular structure can be made out, and 

 these may be formed of hyaloplasm alone. In that case, this must be looked upon as the 

 essential part of protoplasm. So far as amoeboid phenomena are concerned, it is certainly so ; 

 .but whether the chemical changes which occur in many cells are effected by this or by 

 spongioplasm is another matter. 



The movements within plant cells must also be regarded as due to the flowing of hyaloplasm. 

 It is, indeed, impossible to conceive that the contraction of a reticulum could produce the 

 circulation of the protoplasm which is seen within a cell of Vallisneria. How the flowing is 

 produced is an entirely diiferent question, and one which must at present remain unanswered. 



Quincke has shown that if a drop of solution of albumin surrounded by an envelope of 

 oil is placed in water a soapy film forms at the junction of the oil and water, and the drop 



1 Carnoy and many other histologists have assumed that the spongioplasm or reticulum is the con- 

 tractile part of protoplasm, and that the hyaloplasm is passive. If this were the case electrical excitation 

 should cause the reticulum to shrink and to squeeze the hyaloplasm out of its meshes whereas the con- 

 trary is the case, the hyaloplasm passes into the meshes of the spongioplasm, which become thereby 

 enlarged. 



2 In dealing with the structure of muscle it will be shown that here also as in protoplasm there is a 

 passage of a substance resembling hyaloplasm into and out of a porous spongioplasm. It will further be 

 presently shown that the activity of cilia, can also be explained by assuming a flowing of the cell -hyaloplasm 

 into and out of the cilia, so that all these forms of contractile phenomena can be brought into the same 

 category. 



