III.] THE PROTEUS ANIMALCULE. 19 



enables its particles to hold together and form a continuous 

 sheet, but permits a rod to be passed into or through the 

 bubble without bursting it; the walls closing together, and 

 recovering their continuity, as soon as the rod is drawn away. 



It is this property of the ectosarc of the Amoeba which 

 enables us to understand the way in which these animals 

 take in and throw out again solid matter, though they have 

 neither mouth, anus, nor alimentary canal. The solid body 

 passes through the ectosarc, which immediately closes up and 

 repairs the rent formed by its passage. In this manner, the 

 Amcehce take in the small, usually vegetable, organisms, which 

 serve them for food, and subsequently get rid of the un- 

 digested solid parts. 



The chemical composition of the bodies of the Amcehce 

 has not been accurately ascertained, but they undoubtedly 

 consist, in great measure, of water containing a protein com- 

 pound, and are similar to other forms of protoplasm. They 

 absorb oxygen and give out carbonic acid, and the presence 

 of free oxygen is necessary to their existence. When the 

 medium in which they live is cooled down to the freezing 

 point their movements are arrested, but they recover when 

 the temperature is raised. At a temperature of about 35° C. 

 their movements are arrested, and they pass into a condition 

 of " heat-stiffening," from which they recover if that tempera- 

 ture is not continued too long ; at 40° to 45° C. they are killed. 



Electric shocks of moderate strength cause Amcehce at 

 once to assume a spherical still form, but they recover after a 

 while. Strong shocks kill them. 



Not unfrequently, an active Amoeba becomes still spon- 

 taneously, acquires a rounded form, and secretes a structure- 

 less case or cyst, in which it remains enclosed for a shorter 

 or longer period. 



If AmoebcB are not to be found, their nature may be 

 understood by the examination of bodies, in many respects 



2—2 



