LIVING SUBSTANCE 



129 



interesting task for the physiologists to investigate carefully these 

 phenomena, heretofore so ill-defined, to prove by refined methods 

 what vital phenomena are really depressed and to what degree, and 

 finally to show how this voluntary apparent death, which, it is 

 widely believed, has in it absolutely nothing mystical, is to be 

 explained physiologically. 



How little justification there is in doubting the power of certain 

 organisms to retain the capacity of life without exhibiting the 

 slightest vital phenomena, and even for so long a time that the 

 usual duration of their life is greatly surpassed, appears when we 

 turn from the vertebrates to the invertebrates, which have been 

 very carefully investigated in this respect. 



Leeuwenhoek (1719) made the very remarkable observation 

 that in the dust of eaves-troughs animalcules exist which are 

 capable of drying up completely without losing the power of 

 awakening to active life upon being moistened with rain- 



FIG. 41. Macrobiotus Hufdandi, -A tardigrade, a, Creeping, in the living state. (After [R. 

 Hertwig.) b, Dried, in the state of apparent death. 



water. Since their discovery by Leeuwenhoek this fact has been 

 confirmed by a great number of observers and its details have 

 been more fully described. It is not difficult to convince one's 

 self of its truth. If some of the crust be scraped from an old 

 eaves-trough or from the moss-covered side of an old tree-trunk, 

 and the dry powder be covered with pure rain-water, often in the 

 course of some hours a number of small animals can be seen by 

 the aid of the microscope, actively creeping about among the 

 particles of mud. They are mostly representatives of the wheel- 

 is 



