34 



PROTOPLASM AND THE CELL 



has done more to render superfluous any doctrine of a "vital force" 

 than the development of our knowledge concerning the importance of 

 these simple chlorides, phosphates, carbonates, and sulphates of calcium, 

 magnesium, sodium, and potassium. Just as surely nothing could do 

 more to indicate the extreme complexity of vital reactions than the appar- 

 ent need of including them as well as proteid and carbohydrate in our 

 list of the components of the huge mass of molecules characterizing life. 



FIG. 7 



PROTOPLASMIC FUNCTION. 



The next part of the general physiology of protoplasm is naturally a 

 description of its basal functions. We shall examine at present, then, in 



the merest outline only, those pro- 

 cesses common to all protoplasm and 

 try to learn what conditions and 

 uses underlie its structural nature. 

 We may conveniently, but somewhat 

 arbitrarily, make four classes of the 

 functions of protoplasm: (1) respi- 

 ration, (2) nutrition, (3) irritability, 

 and (4) reproduction and growth. 

 Within these four types of organic 

 activity may logically be included 

 all the various processes character- 

 istic of the tissues of animals. 



Respiration. Respiration is a func- 

 tion common to all that lives, to 

 plants as well as to animals. It con- 

 sists essentially of the taking in of 

 oxygen and the throwing out of 

 the products of the oxidation of the 

 tissues, largely carbon dioxide and 

 water. This function is one of the 

 most fundamental of all vital pro- 

 cesses, oxidation being the most uni- 

 versal of all the chemical changes in 

 protoplasm. This union of oxygen 

 with the tissues of animals and of 

 plants furnishes the basis of the met- 

 abolism which is their life. Proto- 

 plasm respires inevitably and always. 

 In the minute animals, especially 

 those in the water, ameba, for ex- 

 ample the change takes place directly between the protoplasm and the 

 environment. In the higher animals, however, some mechanism is neces- 

 sary for bringing the oxygen to the protoplasmic cells in the interior of the 



Hydra. A fresh-water species from France, 

 the tentacles fully expanded. On the right 

 side of the trunk is seen a budding daughter- 

 hydra. (Dubois.) 



