30 INTRODUCTION TO CYTOLOGY 



exhibit singly the phenomenon of isomerism, this number is seen to be 

 incalculable. For example, it was shown by Miescher that an albumin 

 molecule with 40 carbon atoms could have about 1,000,000,000 isomers, 

 and some albumins probably have more than 700 carbon atoms. Albu- 

 min, moreover, is only one of many complex substances present in proto- 

 plasm. Hence, the statement that all living cells are composed of the 

 same substance, protoplasm, is true only in a general sense. Although 

 they are made up of the same categories of substances existing in the 

 same general type of organization, the protoplasms of different organisms 

 vary widely in the relative amounts of these leading constituents. For 

 example, the fats and lipides are relatively more abundant in the proto- 

 plasm of animals than in that of plants. The carbohydrate-protein 

 ratio also shows notable differences in the two kingdoms, carbohydrates 

 being relatively more abundant in plant protoplasm. ^^ Qualitative 

 differences are no less significant. The carbohydrates, which in plants 

 are chiefly pentoses and in animals chiefly hexoses, may be cited. Analo- 

 gous 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 by Kossel, E. T. Reichert, and a 

 number of other writers upon the relation of this great diversity in the 

 constitution of protoplasms to the amazing variety observed among 

 living organisms. Reichert and Brown (1909) have shown that each 

 animal species examined has its own characteristic type of haemoglobin, 

 and that relationships may be indicated by degrees of similarity in the 

 crystals of this substance. The same situation is found in the case of 

 starch in plants (Reichert, 1913, 1919). That the specificity of organisms 

 is largely a matter of protein diversity is strongly indicated by the 

 phenomena of immunology. ^^ At the same time the importance of 

 structural diversity must not be forgotten. 



In concluding this section, the general significance of the results of 

 analyses of protoplasm by chemical methods should be considered. It 

 cannot be maintained that anything like an adequate chemical picture of 

 living protoplasm has been obtained. As A. Meyer (1920) and others 

 have pointed out, such analyses include ergastic reserves and by-products, 

 which differ in amount and kind at different stages of the metabolic 

 cycle. Furthermore, in such a complex and delicately balanced system 

 as protoplasm the analytical methods employed can scarcely fail to induce 



^^ E.g., compare the analyses of Sabellaria eggs (Faure-Fremiet, 1921) and Zea 

 pollen (Andersen and Kulp, 1922, 1923). 



" See Reichert (1914) and R. S. Lillie (1923; Chap. Ill and literature there cited), 

 also the discussion by G. Reed (1923). 



