72 BIOLOGY: GENERAL AND MEDICAL 



comprised the little walk about the room, yet all the 

 time he sat quietly in the chair, there were going on within 

 his body a great number of invisible movements, for the 

 heart was continually beating, the blood and lymph were 

 continually circulating, the function of digestion was 

 probably in progress with its involved movements of 

 secretion, muscular contraction, absorption, excretion, 

 etc., and during all this time the cells of the entire body 

 were more or less actively nourishing themselves, their 

 cytoplasm continually flowing to and fro in rhythmical 

 currents. 



We are accustomed to think of plants as motionless 

 things, yet to one who has come to the realization of 

 what plant life really means a growing plant is full of 

 energy. There are currents of sap ascending the stems 

 and flowing into the leaves, bringing to these great cellu- 

 lar laboratories the nutritious substances absorbed by 

 the rootlets from the soil. As the sap comes in it is 

 absorbed by the active cells which work it over, extract- 

 ing useful substances, manufacturing new compounds, 

 and then sending these away in currents, sometimes to 

 the flowers, sometimes to the seeds, and sometimes to 

 the roots where the newly prepared compounds, changed 

 or unchanged, are stored up for future needs. Add to 

 this the continuous accession of new cells by multiplica- 

 tion of those already present, the necessary gaseous and 

 nutritional changes by which the substance of the cells 

 is itself kept alive, and we find the plant, seeming all the 

 while to be inactive, full of life and motion. 



Cytoplasmic Circulation. This form of movement is in 

 constant progress in every active cell. It is most active 

 and most easily observed in young cells, especially 

 vegetable cells, such as are found in the hairs of Trad- 

 escansia, which are very soft and moist, and in the 

 amceba. It consists in a regular flowing motion of the 

 cytoplasm within the confines of the cell and subserves 

 the double purpose of affording all portions of the pro- 

 toplasm an opportunity of coming into contact with 



