INDEPENDENCE OF CELLS. 3 



The discovery of Siebold,* that the vitelline spheres of the 

 egg of the Planarise exhibit alternate contractions and dila- 

 tations, which, under favourable conditions, continue for hours, 

 and the various subsequent discoveries of similar movements, 

 or changes of form occurring in the colourless blood corpuscles, 

 in pigment cells, and elsewhere, have led Kollikerf to express 

 the opinion that the contents of all cells are contractile. 



Virchow^: gave a still more precise expression of opinion 

 when he stated that ciliary movement is to be attributed to a 

 contractile substance ; to which conclusion he was drawn by 

 the discovery that under certain circumstances these move- 

 ments, after having ceased, could again be excited by dilute 

 solutions of the fixed alkalies. 



Leydig referred to the significance of the movements occur- 

 ring in the spherules of the yolk, which he, in common with 

 Ecker, regarded as evident phenomena of life. 



Kiihne|| undertook a series of comparative physiological and 

 chemical researches on muscular substance and sarcode, and 

 pointed out the similarity of the phenomena they presented in 

 the act of dying. 



By all of these, however, the sarcodal substance was regarded 

 as something different from animalcules, and as a material sui 

 generis. 



Max SchultzelT was the first to show that sarcode is 

 analogous to the body or contents of animal cells, and that 

 on this account the infusorial animalcules possessed of inde- 

 pendent life were simple or compound (fused inter se) cells. 

 Schwann's views received support from these statements. 

 According to the new doctrine, the cell was the typical form 

 element of nearly the whole organic kingdom. The previous 

 inquiries on the contractile sarcode could now be applied to 

 the knowledge of the animal cell, and the renewed parallel 



* Froriep. Notizen, No. 380, p. 85. 

 t Wiirzburg. Verhand., Band viii. 

 | Virc how's Archiv, Band v. 

 Handbuch der Histologie, 1856. 

 !| Miiller's Archiv, 1859, p. 817. 

 51 Muller's Archiv, 1861, p. 17. 



