CHAPTER IX 



GENERAL CONSIDERATIONS ON THE EFFECTS OF CHEM- 

 ICAL AND PHYSICAL AGENTS UPON PROTOPLASM 



IN the present chapter it is proposed to consider certain 

 general matters upon which the facts given in this First Part 

 throw light : namely, (I) the structure and composition of 

 protoplasm ; (II) the limiting conditions of metabolism ; 

 (III) the dependence of protoplasmic movement upon metabo- 

 lism and external stimuli ; and (IV) the determination of the 

 direction of locomotion. 

 / 



1. CONCLUSIONS ON THE STRUCTURE AND COMPOSITION 

 OF PROTOPLASM 



The question of the structure of protoplasm is preeminently 

 a histological one. Microscopical study ^nust eventually be re- 

 lied upon to settle it. However, the results of experimental work 

 seem to favor, as we have already pointed out (p. 70), BUTSCHLI'S 

 view of a honeycomb, or foam structure, of protoplasm. 



The problem of the constitution of protoplasm is, on the other 

 hand, preeminently a chemical one, and it must be solved by 

 experimental methods. Our results can lead us to certain 

 qualitative statements on this matter. 



The chemical composition of protoplasm is immensely com- 

 plex. Just as the geologist is forced by the facts to assume a 

 vast, but not infinite, time for earth building, so the biologist 

 has to recognize an almost unlimited complexity in the consti- 

 tution of protoplasm. 



The evidence that protoplasm is so complex is gained partly 

 from the results of micro-chemistry. Many staining fluids act 

 upon only a small part of the protoplasm of a single cell, so 

 that a mixture of stains may be used, each component of which 



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