368 LIFE : OUTLINES OF GENERAL BIOLOGY 



The definition of this idea was largely due to Max Schultze in 18O1, 

 who was kd from his studits of Protozoa to recognise that through- 

 out all organisms the fundamental common basis is the \'iscid iiuid 

 which Dujardin had called "sarcode" and von Mohl, following 

 Purkinje, had called "protoplasm". It was von Mohl's name that 

 survived to denote what Huxley conveniently described as "the 

 physical basis of life". 



Hy protoplasm is meant the complex material that is essentially 

 concerned with vital processes, and it is generally regarded as a 

 mixture of substances which owe no small part of their virtue to 

 their inter-relations with one another. It must be understood, how- 

 ever, that there may be many materials in a cell that are not to be 

 included as part of the "living matter" or protoplasm. Thus therr 

 may be pigment granules, starch grains, crystals, globules of oil, 

 vacuoles of water, and so on, which ore not within the charmed 

 circle of protoplasm. If the whole cell-substance be called cytoplasm 

 and the relatively unessential granules and vacuoles, often of known 

 chemical composition, be called inetaplasm, then a good w^orking 

 definition of protoplasm would be "cytoplasm minus metaplasm". 

 Examples of relatively pure protoplasm may be found in many 

 minute egg-cells without yolk, as in sea-urchins, in blood corpuscles, 

 in pollen grains, and in such simple organisms as Flowers-of-tan 

 (Mj'xomycetes) and Amoebae. 



The student is familiar with the appearance of cells in sections 

 that have been prepared for the microscope, and readers working 

 by themselves should either make or purchase some typical pre- 

 parations to show the structure of the cell. We give a short list of 

 convenient objects for examination. 



The egg-cells of star-fishe.s and The green threads of Spirogyra 



sea-urchins. from the ditch. 



The blood of the frog. The hairs of the stamens of 

 Section through the ovary of a Tradescantia. 



mouse. The epidermis stripped oflf a leaf. 



The study of fresh material is often very disappointing, since at 

 first one sees so little; and thus recour.sc is had to methods of 

 fixing, staining, and clearing which bring out fine details of structure 

 in the cell. The fresh specimen is first treated with a "fixative", such 

 as osmic acid, corrosive sublimate, or formaldehyde solution — 

 agents which have the property of causing what was originally a 

 sticky fluid to "set" into a more or less firm jelly. The next step 

 is cutting, cither with a razor or a microtome, and this usually 

 succeeds best when the object has been steeix^d in liquid paraffin, 

 celloidin, or some other penetrating material that soaks in and fills 

 up all the minute interstices, afterwards sohdifying when cooled. 



