Protoplasm is commonly seen to be a colorless, pale, milky, semi-translucent substance, more or less altered in appearance by various foreign matters lying in it. These latter also give it a granular appearance, and when dead it commonly exhibits a linear marking or fine network. During life its consistence is nearly fluid, varying with the circumstances in which it is placed, from that of a gum solution to a soft jelly. When living unmolested in its normal medium it seems to flow into various shapes, but this is a living action which does not prove it to be diffluent, for any attempt to investigate it by experiment causes a change in its consistence approaching to rigidity.

As the full comprehension of the function of this substance lies at the root of the greater part of Physiology, the reader is referred for a detailed account of its properties to Chapter III (Chemical Basis Of The Body), on Vital Phenomena, where it will be discussed at greater length.