BIONOMICS 239 



day, the latter being open and kept at the ordinary tempera- 

 ture, hydrocyanic acid is formed." Again we may infer that 

 a metabolic disturbance in particular, surfeit of nitrogen 

 (in-feeding) is apt to diminish the bio-chemical and bio- 

 economic value of plants. 



We have already referred to the fact that it is only when 

 put together in certain proportions that sulphur, charcoal, and 

 nitre produce explosives which may have devastating effects. 

 In other proportions they are calculated to fertilise the soil and 

 to feed populations, and it is the quasi-symbiotic relations sub- 

 sisting between nations that determine whether the particular 

 materials shall be put to fruitful or frightful use, whether they 

 shall help to feed and fertilise or devastate and destroy. In 

 all cases it is the matter of mutual relations that determines 

 effects and values. 



It is remarkable that the toxicological effect of many plant 

 alkaloids is especially marked upon the respiration of animals 

 (see example of Coriamyrtin and Tutin, British Association 

 Eeport, 1912, p. 643), and when we remember the importance 

 of respiration in biological symbiosis, we may again say that 

 the plant here effects pathologically (by extreme stimulation) 

 what in normal relations it effects physiologically (by mild 

 stimulation), i.e., normal respiration is based on undisturbed 

 symbiosis. 



It is similar in the allied case of circulation, on which so 

 much depends in life and in evolution. Darwin, as we have 

 seen, mentions in the Origin of Species the belief held by 

 physiologists that "the brain must be bathed by warm blood 

 to be highly active, and this implies aerial respiration." 



He omits, however, entirely to consider to what an extent 

 both circulation and respiration depend on biological 

 symbiosis. (That they do so depend, and this very importantly, 

 we have already inferred in this and in the first chapter). 



He concludes that " warm-blooded mammals when inhabit- 

 ing the water lie under a disadvantage in having to come 

 continually to the surface to breathe." This is, indeed, what 



