10 GENERAL BIOLOGY 



organisms as liquids that contain solid matter rather 

 than as solids with a percentage of liquids. The 

 large amount of water in protoplasm is a very im- 

 portant and significant feature of its make-up, 

 since it affords a means for the transfusion of sub- 

 stances from one part of the animal or plant to 

 another, and gives the organism a certain necessary 

 plasticity as well. 1 



The combinations of carbon (C), oxygen (O), 

 hydrogen (H), and nitrogen (N) that make up the 

 bulk of protoplasm fall into three great groups or 

 classes, the proteins or albumens, the carbohydrates 

 (sugar and starches), and the fats. These three 

 groups are much more easily described than defined. 



The Proteins are found in all protoplasm and are 

 indispensable to the processes of life. They consti- 

 tute a large and diverse group differing widely one 

 from another, but all sharing certain group charac- 



1 Recent advances in physical chemistry have thrown much light on 

 the physical and chemical processes of protoplasm. It has been dis- 

 covered that, in great dilution, many chemical substances tend to dis- 

 sociate into ions, as e.g. NaOH into Na and OH, each ion consisting, in 

 the current explanation, of an atom or atomic group bearing a charge of 

 negative or positive electricity. As a rule, it is only in this dissociated 

 condition that atoms are active in combining with one another. It has 

 been found by experiment that the effect of certain salts on protoplasm 

 (for instance the poisonous action of the heavy metals) is in direct pro- 

 portion to the ionization of the salts. It has been shown also that cer- 

 tain salts are absolutely essential to life processes, although the amount 

 required may be very minute. A fresh-water crustacean, Gammarus, 

 according to W. Ostwald, inevitably dies if placed in absolutely pure 

 distilled water, but will live indefinitely if a trace of common salt 

 (NaCl) be added. The amount necessary is only eight ten-thousandths 

 of a gram (twelve thousandths of a grain, Troy) to a liter of water. 



