262 SCIENCE PROGRESS 



intoxications of the organism tend to modify the protoplasm, 

 it remaining to be seen which feeding habits are the most 

 calculated to enrich protoplasm and which to impoverish it. 

 Here the autonomy of the organism plays a prominent part in 

 determining the issue. We also know that there exist a number 

 of physiological and biological antagonisms, which remain 

 to be interpreted as to their full sociological meaning. Again, 

 we are led to infer increasingly every day that health depends 

 pre-eminently upon biological support, such as that of phago- 

 cytes and other symbiotic organisms. What it all points to 

 is this : that there is a definite sociological order of the 

 universe which, if obeyed, leads to progressive evolution, or, 

 if disobeyed, to degeneration. My thesis is that Symbiosis 

 furnishes the positive and progressive method of life, whilst 

 one-sided exploitation of organism by organism furnishes the 

 negative, degenerative phase of life. 



Let us take another instance of primitive Symbiosis to show 

 that the symbiotic regime tends to produce economic margins 

 much in the same way in which our industrial division of 

 labour produces a constant surplus, rendering possible a maxi- 

 mum of happiness with a maximum of population, i.e. ampler 

 life. 



There is the case of the common fresh-water red alga, 

 Batracho-spermum {B. vagans, var. epiplanorbis), which always 

 grows on the shell of the fresh-water mollusc, Planorbis. The 

 mollusc gains by being protected from enemies, being densely 

 clad with the alga, and is also able to live in places which 

 would be otherwise unfit for it, owing to poverty of oxygen 

 and excess of carbon dioxide, the former gas being supplied, 

 and the latter removed, by the alga. 



In view of these facts, which may again be regarded as 

 typical of the operation of plant-animal Symbiosis, it may 

 be fairly claimed that the symbiotic relation tends to leave the 

 world the better for its presence. In the present example, 

 both the alga and mollusc are decidedly better off for their 

 Symbiosis, The more Symbiosis between them, the less need 

 of predaceous interferences with each other and with other 

 organisms. The point which I wish to stress above all is this, 

 that the symbiotic relation is of more than local significance, 

 that everywhere it makes in an important way for life 

 generally. The presence of symbiotic systems makes, on the 

 whole, for increased economy and increased security of life. 

 In the above case we see, moreover, that the plant, by render- 

 ing animal life possible in an otherwise inhospitable region, 

 assists very materially the diversification of life, which is an 

 important factor of evolution. Darwin insisted, particularly 

 in chap. iv. of the Origin, on the importai;ce of the principle 



