xii PREFACE 



Protozoology in the University of London, to which MY. E. A. 

 Minchin has been appointed. It is recognized that the only way in 

 which we can hope to deal effectually with such diseases as the Sleeping 

 Sickness is by a greatly increased knowledge of the nature and 

 life-history of the parasitic Protozoa which produce those diseases. 



I have to thank Mr. John Murray for permission to reprint 

 the article on Sleeping Sickness, and I am also greatly indebted 

 to scientific colleagues for assistance in the survey of progress given 

 in the second discourse. Amongst these I desire especially to 

 mention Mr. Frederick Soddy, F.R.S., Prof. H. H. Turner, 

 F.R.S., Prof. Sydney Vines, F.R.S., Mr. MacDougal of Oxford, 

 and Prof. Sherrington, F.R.S. To Mr. Perceval Lowell I owe 

 my thanks for permission to copy two of his drawings of Mars, 

 and to the Royal Astronomical Society for the loan of the star- 

 picture on p. 90. 



E. RAY LANKESTER, 



January, 1907. 



