Physiological Studies on Certain Protozoan Parasites. 157 



CONCLUSIONS. 



The general results of the experiments performed is to show surprising 

 differences in the resistance of the parasites of Diadema to various unfavor- 

 able conditions. In some cases the most resistant form may live several 

 hundred times as long as the least resistant one. B is 900 times as resistant 

 to H2SO4 as A , and the difference between B and C with respect to products 

 of decomposition is still more striking. Furthermore, a form which is 

 strongly resistant to one condition may be only feebly so to another, and 

 vice versa. For example, 5 is 8 to 10 times as resistant to H2S as C, but 

 1,500 times less resistant to certain of the products of decomposition of 

 Diadema tissues. C is more resistant to CO2 than A or D, but less resistant 

 to H2S. A, C, and D are 24 to 450 times more resistant to KOH than to 

 H2SO4, while B is somewhat less resistant. Other similar facts could be 

 mentioned. 



Comparing all of the results obtained, it is therefore seen that the similar 

 habit of life of the four forms in question has not brought about physio- 

 logical similarity except in certain adaptive characters which are a sine 

 qua non for continued existence in the same host (e. g., ability to resist the 

 digestive juices of the latter, etc.). In other respects they are just as 

 different as almost any four free-living forms that might be selected and 

 so far as the evidence of these experiments goes it seems to show that the 

 physiological characters of an organism are not merely the result of its 

 environment, but may be as fundamental and characteristic as its morpho- 

 logical ones. 



