44 ESSENTIALS OF ZOOLOGY 



fuses sloAvly or not at all through animal membranes. It changes 

 from a fluid or sol state to a more solid or gel state and may return 

 in the other direction. Ordinarily the viscosity of the continuous 

 phase or supporting liquid is only three or four times that of water, 

 while with the dispersed particles included it is only eight or ten 

 times that of water. The viscosity of the nuclear fluid is only twice 

 that of water. Since glycerin has a viscosity about a thousand times 

 as great as water, it will be realized that most protoplasm is quite 

 fluid in its active state. Changes in viscosity accompany and are 

 essential to the activity and functioning of it. 



Protoplasm is not a single compound; it is a colloidal system of 

 a number of chemical compounds existing together. Colloidal systems 

 are known as disperse systems of the emulsoid type. The more 

 watery or continuous part of the system is known as the dispersion 

 medium, while the particles or molecular aggregations constitute 

 the dispersed phase. An important consequence of the colloidal 

 systems in protoplasm is the enormous surface of particles exposed 

 to the continuous phase. If a sphere of material has a radius of 

 one centimeter its total surface will be 12.6 square centimeters. 

 Now, if the same volume of material is in colloidal particles of the 

 average size given above, the total surface of these will be approxi- 

 mately 7,000 square meters. This increase in surface is one of the 

 significant effects of colloidal organization of substances, because 

 many important reactions occur at these surfaces. By the presence 

 of salt ions in the continuous phase and these becoming adsorbed 

 upon the surfaces of the colloidal particles, they acquire an electric 

 charge. Protoplasm exhibits these several phenomena because of 

 its colloidal nature. 



Chemical Nature of Protoplasm 



Up to the present time, protoplasm has eluded complete and 

 exact chemical analysis. Nevertheless the compounds of living 

 matter are composed of several elements, many of them the most 

 ordinary and abundant in the world. The list of elements necessary 

 to make human protoplasm could be gathered in almost any locality 

 on the face of the earth. As a rule the elements found in protoplasm 

 are oxygen, carbon, hydrogen, nitrogen, sulphur, phosphorus, cal- 

 cium, sodium, chlorine, magnesium, iron, potassium, iodine, and fre- 

 quently others like silicon, aluminum, copper, manganese, bromine, 

 and fluorine. The most abundant of these are found named in the 



