152 THE MENDEL JOURNAL 



and others. But are we quite sure we know the full 

 extent of its operations in Nature ? It cannot yet be 

 said just what link it makes in the chain of Nature's 

 work. Suppose we shall succeed in eliminating it, 

 have we yet thought out the possible consequences ? 

 It is well not to forget the fact cited by Darwin, 

 that the combs and nests of humble bees are destroyed 

 by field-mice and these by cats. If, therefore, the 

 people of a particular village, who are pestered by cats, 

 destroyed every one they could, they would reap, 

 as an unexpected and unpredictable consequence, 

 the loss of their honey harvest. No one had ever 

 imagined that there could be any relationship what- 

 ever between the presence of cats and the production 

 of honey. But it is so. When the cats are des- 

 troyed, the mice will multiply, and these will raid 

 the stores of honey carefully preserved by the bees. 

 When the cats multiply the mice will be destroyed 

 and the honey will be. saved. There is more even 

 in the concrete facts of Biology than is dreamed of 

 in the abstractions of Metaphysics. 



But let us grant that the tsetse fly is a malign 

 agent. Is there nothing of good which it has 

 achieved ? It appears to have evolved a race of 

 wild cattle in Africa which is indifferent to its 

 bite, since the individuals of that race have 

 their blood swarming with the trypanosomic germs 

 conveyed by the fly, and yet these cattle are healthy 

 and vigorous. There has thus been evolved a race 

 of cattle happy and strong in spite of the trypano- 

 somes and the tsetse flies. Just as in Malta there has 



