Xll PREFACE 



formed the subject of my paper in The British Medical 

 Journal of May 5, 1906, on "The Diffusion of Red 

 Blood-corpuscles through Solid Nutrient Agar." The 

 reason why the diffusion had not been previously 

 observed was that one does not usually endeavour to 

 obtain cultures from the blood at 60 C., nor should 

 I have done so had it not been for the zeal of the 

 "young gentleman." 



In January, 1906, before my paper was published, I 

 was demonstrating this remarkable diffusion of red cells 

 through the agar to my brother, Professor Ronald Ross, 

 at Liverpool, by placing some blood under a cover-glass 

 on a film of agar jelly spread on a slide. He was 

 impressed by the way in which the cells became spread 

 out between the cover-glass and the surface of the agar 

 film, and he suggested that it would be a good means 

 for blood-examination by the microscope, for the 

 corpuscles became admirably arranged and spread out in 

 such a way that each could be critically examined. 

 Then he remarked a remark which has led to all the 

 researches described in this book, and to the discovery 

 that mitotic divisions in human cells are induced by 

 chemical agents "I wonder what would happen if we 

 were to mix some stain with the jelly and then place 

 the living cells on it under a cover-glass." This sugges- 

 tion was promptly put into operation, and fortunately 

 (because it was the best which could have been chosen) 

 the first stain experimented with happened to be poly- 

 chrome methylene blue, with w r hich I obtained results 

 which determined me to adopt this method of examina- 

 tion to the exclusion of all others. 



