VITAL PROPERTIES OF CELLS 17 



(c) Molecular n/o/i/i/i/ is a dancing or oscillatory movement of thr 

 irniimlrs in living protoplasm. Such granules may be non-living matter. 

 pigment, etc. This typo of motion is also called brow man movement. 

 It is probably purely a physical phenomenon. It may be simulated by 

 mixing finely divided carmin with glycerin. 



(d) Circulatory or streaming movement is present in various de- 

 grees in probably all living protoplasm. It is only when it is rapid 

 that it becomes easily discernible. It is readily demonstrable in certain 

 cells, e.g., chara and nitella; also less readily in certain protozoa (Para- 

 mecium). It must most probably be interpreted as a form of respira- 

 tion. It is characterized by a flowing 



or streaming of the protoplasmic gran- 

 ules in a definite direction. 



(e) The reason for listing muscu- 

 lar as a separate type of motility is 

 mainly its predominance in animals 

 and the fact that it does not apparently 

 fully conform to any of the above types. 



It is characterized by a reversible FlG . 2 3,-CiLiATE AND FLAGKLLATE 



process of contraction of specially dif- CELLS. 



ferentiated muscle fibrils. It perhaps A, ciliated cells isolated from the 



most closely resembles streaming motil- trachea of a cat; B, human sperm*- 



.. T,L i -i j. i ^ tozoa 1. in surface view; 2, in 



ity. It leaas to least confusion, m view profile ' Examined fresh in ' norma i 



of our present lack of definite knowl- saline solution. X 550. 

 edge regarding the physical and chem- 

 ical phenomena underlying muscular motion, to speak of it as a distinct 

 type. It will be further discussed under Muscle. 



(4) Reproduction. The essence of reproduction is cell multiplica- 

 tion. A living cell has the power of producing other cells like itself. 

 Viewed philosophically, cells may conceivably arise in two different ways: 

 (1) from non-living material, spontaneous generation (abiogenesis) ; (2) 

 from preexisting cells by division. Science has quite generally accepted the 

 aphorism 'omnis cellula e cellula' (Virchow) as an expression of the 

 whole truth. However, full acceptance of the doctrine of evolution logi- 

 cally compels belief in spontaneous generation : this not in any such 

 crude form as that frogs may arise from the mud of rivers, or insect? 

 from dew or dung, but that given the conditions (conceivably possible 

 somewhere in the universe to-day) prevalent when life first appeared as 

 the original mass of living protoplasm, the 'cytode' or 'cytoblastema,' the 

 inorganic may continually be passing into the primarily organic, e.g., 

 3 



