THE STRUCTURE OF PROTOPLASM 241 



(Figs. 28, 115). It is also typical of some nuclei such as the 

 macronucleus of Euplotes and the nuclei of amphibian (Triton 

 and Cryptobranchus) red blood cells (Fig. 117). How alveolar 

 protoplasm results from an emulsion under pressure is indicated 

 in Fig. 118, where A schematically represents the usual proto- 

 plasmic emulsion; B, alveolar spheres; C or D, alveolar proto- 

 plasm; and E, a possible orientation. The alveoli become 

 pentagonal and line up in very symmetrical order when adjoining 



if, # 



B 



.XX. vW 



C D E 



Fig. 118. — Five possible arrangements of globules in an emulsion. 



an outer surface or a larger foreign particle in protoplasm (Fig. 

 115). 



The criticism that has been directed against the alveolar 

 hypothesis cannot be based on the contention that the structure 

 is an artifact. This form of criticism arose from work by Hardy 

 and Fischer, who showed that an alveolar structure can be 

 produced in gelatin by treatment with certain reagents. It was, 

 therefore, maintained that the structure is artificially produced 

 in protoplasm. This is not wholly true. Biitschli's error did not 

 lie in the observation of artifacts but merely in claiming a uni- 

 versal occurrence and fundamental value for the structure that 

 he saw, in both living and nonliving material. An alveolar 

 structure occurs in protoplasm but not in all protoplasm and 

 not in gels. 



The alveoli of protoplasm are probably minute vacuoles, for 

 vacuoles are very abundant in protoplasm — more so than usually 

 realized. Chamberlain has suggested that most emulsion, 

 alveolar, and like structures of protoplasm are all modifications 



