CONDITIONS GOVERNING PROTOPLASMIC MOVEMENT. 



83 



of water, and consequently with the increase of volume and decrease in 

 the index of refraction of the protoplasm. As the maximum amount of 

 water becomes approached the spherical form is assumed ; so that, there- 

 fore, distilled water, as pointed out in the section on imbibition, kills 

 protoplasm, possibly by the extraction of the salts which are necessary- 

 for the life of protoplasm. Thus, salt-water fish are killed by placing in 

 fresh water; the fresh water is then found to increase in its inorganic 

 constituents, which thus evidently must be extracted from the tissues 

 of the animals with which it is in contact. So also desiccation produces 

 shriveling of the protoplasm and an entire disappearance of all power of 

 movement, although in the lower forms of life vitality is not destroyed, 



FIG. 53. AM<EBOID MOVEMENT IN A COLORLESS BLOOD-CORPUSCLE OF THE 

 FROG. (Engelmann.) 



The temperature was gradually raised from atom, and then gradually reduced. 



but becomes latent ; and when the proper percentage of moisture is again 

 supplied the protoplasm will regain its power of contracting. 



This is seen in the infusoria and various low forms of animal and 

 vegetable life, which may be preserved indefinite! jr when desiccated, and 

 ma}* be restored to active life by placing them in a condition to absorb 

 moisture. 



3. TJie Supply of Oxygen. Protoplasmic movements require the 

 constant supply of oxygen, although they may continue to live in a 

 medium of much lower oxygen-tension than is seen in the atmosphere. 

 Higher tensions of oxygen than are found in the atmosphere will reduce 

 the motions of protoplasm, which are, however, again renewed when the 



