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INTRODUCTION 



The physical basis of all life, both vegetable and animal, is 

 called protoplasm. The vital substance forming the most highly 

 developed animals differs in degree rather than in kind from the 

 undifferentiated protoplasmic mass composing the most simple 

 form of life known. Protoplasm is a semi-fluid, transparent, 

 viscous substance, which occurs usually in small indixadual par- 

 ticles, called cells. Sometimes it seems to be quite homogeneous 

 but more often a reticulated structure can be detected. A study 

 of its composition reveals that its most abundant constituent is 

 water, which amounts to 75 per cent, of the whole material. The 

 remaming 25 per cent, is made up of solids which consist chiefly 

 of nitrogenous compounds called proteins, but certam metals 

 (potassium and calcium) as well as phosphorus and sulphur are 

 also present in a combined form together with small quantities 

 of fats and carboh3'drates. 



An elementary knowledge of the physiolog}^ of protoplasm 

 may be gamed by stud^dng the vital manifestations of the 



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Fig. 1. Amoeba (after Graves, from Shipley and MacBride). 

 1 Nucleus, 2 Contractile vacuole throu{i;li which waste pro- 

 ducts are excreted, 3 Pseudopodia, 4 Vacuoles containing 

 food, 5 Grains of sand. 



amoeba. This is a minute organism found in stagnant water, 

 and resembling, when seen under the microscope, a little lump 

 of moving jelly. It can be observed to move about spontaneously. 



