rROTOPLASJMIC STRUCTURE 69 



of the colloidal composition of the system and not expres- 

 sions of any distinctively vital condition or structure. 

 He and others have demonstrated that similar appear- 

 ances can be produced by fixation in a])parenllv homo- 

 geneous colloidal solutions or gels (egg-white, gelatine).* 

 Hardy also pointed out various parallels between the 

 processes of gelation in artificial colloidal systems and the 

 changes of physical state in living protoplasm.' From 

 these and related facts it became clear that if we are to 

 draw conclusions regarding protoplasmic structure from 

 the appearances seen in microscopic preparations, the 

 general nature of the changes produced in colloidal 

 systems by physical and chemical agents must first be 

 determined. Great impetus w^as thus given to the 

 study of the physics and chemistry of colloids, a subject 

 then in its early stages, and also to the study of the 

 structure and physical properties of protoplasm in the 

 living condition. 



Various resemblances between living protoplasm and 

 emulsions were long ago described by Biitschli.-' These 

 resemblances relate both to structure and to certain 

 peculiarities of behavior; e.g., amoeboid movement 

 and modifications of activity b>' changes in the sur- 

 roundings. Biitschli reached the conception that a 

 ''foam structure," corresponding essentially to a film- 

 pervaded or chambered structure, is the t>'])e most 

 generally exhibited by living protoplasm.-* 



» W. B. Hardy, Journal of Physiology, XXXV (1899), 158; cf. also 

 Alfred Fischer, Fixierung,Farbung,u)id Ban des Prolo plasmas, ]cnA (1899). 



2 Hardy, Proceedings of the Royal Society, LX\'I (1S99), 1 10. 



3 Biitschli, Microscopic Foams and Protoplasm. 



4Cf. the discussion by E. B. Wilson, Jour. Morph., X\ (1899), 

 Supplement. 



