12 



A TEXTBOOK OF PHYSIOLOGY 



rit at ion is by no means confined to the living world. Heat and mag- 

 netism cause movements in inanimate matter, and the response of 

 living matter to certain forms of excitation appears to be as inevitable 

 as the lengthening of an iron bar when heated. The unicellular animals 

 move either by flowing out in one or other direction, a part forming a 

 pseudopodium, and the rest following, or by means of vibratile lashes, 

 the cilia, which are set round the circumference of the cell body or 

 at one or other pole. A pseudopodium may be imitated by a capillary 

 tube filled with, mastic varnish. This will extend a pseudopodium 

 towards and eventually engulf a glass fibre wet with alcohol. A 

 glass fibre covered with shellac is taken up by a chloroform drop 

 (Figs. 9Aand9e). 



Movement is excited by the various chemical and physical forms of 

 energy, and may be toward the source of energy or against it 

 positive or negative. The slime fungus, Myxomycetes plasmodium, 



! 



FIG. 9.\. A GLASS FIBRE WET WITH ALCOHOL 



BEING ESGCLFED BY A PSEUDOPODIUM OF 



MASTIC VARNISH. (After Rhumbler.) 



FIG. 9B. A GLASS FIBRE COATED 

 WITH SHELLAC, TAKEX UP 

 BY A DROP OF CHLORO- 

 FORM. (After Rhumbler.) 



forms, by the union of many amoeba-like cells, a sheet of protoplasm 

 which spreads for many inches, over rotten woods. The plasmodium 

 shows marvellous veins in which granular protoplasm streams, with 

 extraordinary rhythm, first in one and then in the reverse direction. 

 The plasmodium flows towards and over its suitable food, digesting 

 and absorbing as it goes. It is atti acted by certain chemical sub- 

 stances positive chemiotaxis. It is repelled by others, e.g., a trace 

 of quinine, or too concentrated a solution of salts, etc. negative 

 chemiotaxis. Similarly, paramcecia or opalina? gather round a drop 

 of dilute acid, and are repelled by dilute alkali. H - ions exert 

 a positive and HO + ions a negative chemiotaxis. Paramcecia exhibit 

 positive galvanotaxis to the negative pole of a constant current. They 

 gather round this pole when the current is passed through the diop 

 of water containing them. Tadpoles turn their hsads toward the anode. 

 They avoid one end of a trough if this be heated to 25-30 C., and seek 

 the cooler end negative thermotaxis. They seek red light and avoid 

 the blue photofaxis. Worms, earwigs, etc., placed in a box with a 



