SUMMARY OF THE CHAPTER 49 



either to the fact that the protoplasm is protected from attack, 

 as is the case with the encysted forms of Protozoa, which are 

 very resistant; or to the fact that the protoplasm is not so 

 readily acted upon by reagents brought actually in contact 

 with it, due to diminished amount of water or other structural 

 modifications ; or, finally, that the protoplasm has a different 

 composition, certain unstable molecules found in other kinds 

 of protoplasm being absent. 



We will now consider the phenomena of diversity in specific 

 resistance of protoplasm. A case of specific low resistance is 

 found in the nervous tissue. Thus many of the alkaloids, e.g. 

 nicotine and cocaine, are almost indifferent to the protoplasm 

 of Protista, but act towards the nervous system as powerful 

 poisons. Hence we are led to conclude that nervous protoplasm 

 contains especially unstable compounds, upon which its action 

 depends. When they are subjected to the action of very weak 

 — towards most substances, indifferent — reagents, extensive 

 and fatal transformations occur. 



Cases of specific high resistance are apparently found in some 

 glands which secrete intense poisons, or in some organisms 

 which live in solutions of some . usually poisonous agent. Ex- 

 amples of this class are tlie HCl-secreting glands of the 

 Vertebrate alimentary tract, the poison-glands of venomous 

 serpents, and the HgSO^-secreting glands of Gasteropoda ; 

 also the vinegar eel, which lives in 4% acetic acid. It ought 

 to be said that it is largely an inference based upon experi- 

 ments on acclimatization, that these glands or organisms will 

 not show a general high resistance. Experiments are needed 

 to determine this point. As to the cause of specific high resist- 

 ance, I believe that much light is gained from the facts of 

 acclimatization, and that any sufficient theory of the latter 

 would serve also to explain the former (see p. 30). 



Under the general poisons we have distinguished four main 

 groups : a. oxidizing poisons ; b. salt-forming poisons ; c. sub- 

 stitution poisons ; d. catalytic poisons. I will comment briefly 

 upon the action of the poisons of each of these groups. 



a. Oxidizing Poisons. — The ordinary oxidation processes in 

 living protoplasm involve the consumption not of the proto- 



