42 INTRODUCTION TO CYTOLOGY 



protein ratio also shows notable differences in the two kingdoms. Ana- 

 logous differences also exist between the smaller plant and animal groups, 

 and with these differences in chemical constitution are associated many 

 characteristic diversities in metabolic activity. Thus it is not simply 

 with protoplasm but with protoplasms that the working biologist has 

 to deal. 



Special emphasis has been placed upon the relation of this great 

 diversity in the constitution of protoplasms to the amazing variety 

 observed among living organisms by Kossel, Reichert, and a number of 

 other writers. As Reichert states, the evidence seems to indicate that 

 "in different organisms corresponding complex organic substances that 

 constitute the supreme structural components of protoplasm and the 

 major synthetic products of protoplasmic activity are not in any case 

 absolutely identical in chemical constitution, and that each substance 

 may exist in countless modifications, each modification being character- 

 istic of the form of protoplasm, the organ, the individual, the sex, the 

 species, and the genus." With regard to the integration of the various 

 protoplasmic constituents, Mathews (1916) says: "Protoplasm, that 

 is the real living protoplast, consists of a gel, or sol, which is composed 

 of the colloids of an unknown nature which include protein, lipin and 

 carbohydrate. Whether these colloidal particles consist of one large 

 colloidal compound in which enzymes, protein, phospholipin and car- 

 bohydrate are united to make a molecule which may be called a biogen 

 [Verworn 1895, 1903], cannot be definitely stated, but it seems probable 

 that something of the sort is the case." 



The Plasma Membrane. — It was recognized very early that there is 

 at the surface of the protoplast a thin layer of relatively resistant, hya- 

 line protoplasm which Hanstein called ectoplasm, distinguishing it thus 

 from the granular endoplasm within. Pfeffer (1890) employed the cor- 

 responding terms hyaloplasm and polioplasm. The ectoplasmic envelope, 

 which is best seen on "naked" masses of protoplasm, such as amoeba?, 

 myxomycetes, and the zoospores and gametes of algse, has been variously 

 referred to by different writers as the ectoplast, plasma membrane, Haul- 

 schicht, and Plasmahaut. 1 



The proponents of the reticular and fibrillar theories of the structure 

 of protoplasm looked upon this external layer as a region in which the 

 fibrils are more closely compacted or interwoven, whereas Butschli re- 

 garded its relative firmness as due to a compact radial arrangement of 

 alveolae. Pfeffer (1890) held that such a limiting membrane, which 

 living protoplasm always produces on an exposed surface and which 

 consists mostly or entirely of protein substances, is not itself truly proto- 

 plasmic, whereas the majority of cytologists have thought it to be a 



1 A discussion of ectoplasm and endoplasm based upon a large number of ob- 

 servations on Amoeba is given in a new work by Schaeffer (1920). 



