SIGNIFICANCE OF THE CONTEST 237 



the animal world between the highest and lowest 

 forms of life ; discoveries which, moreo\'er, proved that 

 disease in man was but the signal of the victorious 

 progress of the microbe through our tissues. 



In the study of parasitism, however, we are pre- 

 sented with an e\'en still more real and more highly 

 organised contest. We now know that the parasites, 

 which we hiive studied in the preceding chapter, with 

 which we, in common with other species of the animal 

 kingdom, have to contend with for our very existence, 

 are members also of the animal kingdom and are 

 governed by the same great laws as those which 

 control and direct the higlier members. The fight, 

 therefore, for supremacy becomes a much more complex 

 and equal one, and therefore more desperate. 



As a matter of fact, we are only beginning to 

 realise the great part which the parasites have taken 

 in bringing about the present distribution of man and 

 animals over the globe. As has been previously 

 stated, we have reason to believe that Africa is to-day 

 inhabited by the primitive races and tlie animals 

 which are found there, largely through the harassing 

 effects of the minute parasites associated with sleeping 

 sickness, malaria, filaria and with the other infective 

 diseases which have infested that continent, most 

 probably from the earliest times. 



In the same way, it is surmised that the present 

 fauna of the New World is the result of parasitism, 

 many of the species which have survived in other 

 parts of the world having perished there in the 

 struggle. This may well have been brought about by 



