A STUDY OF THE MUSCLES 



205 



the presence in the body of great quantities of carbon dioxid, 

 water, and urea. One can often rest to good advantage by 

 changing from one form of activity to another, but from 

 eight to nine hours of sound sleep each night are indispens- 

 able for the health of a growing youth. The necessity for 

 sleep will be further discussed in the study of the nervous 

 system. 



4. A COMPARATIVE STUDY OF LOCOMOTION 



Amoeba. We have already studied the method of loco- 

 motion of amoeba (see p. 24), and we have seen that there 

 are certain cells in the human body 

 (white blood corpuscles) that show a 

 similar amoeboid movement. In all 

 these cells the whole cell body may be 

 said to have a power of contraction 

 something like that seen in highly 

 developed muscle tissue. 



Paramecium. In the group of the 

 Protozoa, or single celled animals, 

 there is another method of locomotion 

 which is wonderfully interesting. If 

 one covers some hay with water and 

 allows the mixture to stand for a few 

 weeks, on examining a drop of this so- 

 called hay infusion one will find a 

 multitude of microscopical animals Fia.96. A Paramecium. 

 that move from one part of the slide 

 to another with great rapidity. By 



c. vac. = contractile vac- 

 uoles (probably for 

 excretion) . 

 adding to the water a drop of gum /. V ac = food vacuoles. 



arabic or other sticky solution, their 

 motions can be retarded so that one is 

 able to make out their form and structure. 



gul. = gullet. 

 mth. = mouth-opening. 



Each par-a-me'- 

 ci-um (for so this animal is called) is a single cell, shaped 

 something like the sole of a slipper. Its whole outer surface 



