26i 
A CASE OF SLEEPING SICKNESS 
STUDIED BY PRECISE ENUMERATIVE 
METHODS : REGULAR PERIODICAL IN¬ 
CREASE OF THE PARASITES DISCLOSED 
BY 
Professor Major RONALD ROSS, F.R.S., 
AND 
DAVID THOMSON, M.B., Ch.B., D.P.H. 
(Read before the Royal Society , 16 June , 1910 ) 
(Received for publication 5 July , I 9 10 ^ 
Prefatory Note by R. ROSS 
For a long time it has appeared to me that much light might 
be thrown on infectious diseases, immunity, and treatment, by more 
exact enumeration of the infecting organisms, and that we might 
even be able ultimately to apply mathematical reasoning to the 
study of these subjects. In 1903* I elaborated a method of blood 
examination, called the thick-film process, which enables us to 
detect small organisms in the blood about twenty times moie easi y 
than in ordinary preparations; but for the lack of the necessary 
assistance I was long unable to apply the method to the laborious 
enumeration of such organisms. Recently, however, the Advisory 
Committee for the Tropical Diseases Research Fund has place 
considerable funds at the disposal of the Liverpool Schoo o 
Tropical Medicine for the study of cases in the tropical ward at 
the Royal Southern Hospital, Liverpool, with the result that the 
investigations referred to were commenced by Dr. David Thomson 
and myself from the beginning of this year. As I expecte 
methodical counting of the parasites has at once veri e or 
disclosed several facts of importance in connection with ma arr 
and trypanosomiasis. We now limit ourselves to a 
description of the remarkable periodical increase of Trypanosoni 
Yates Reports, Vol. V, part I, 1903. 
* Lancet, 10th Jan., 1903, and Thompson- 
