43 
THE PART PLAYED BY PEDICULUS HUM AN US 
IN THE CAUSATION OF DISEASE. 
By GEORGE H. F. NUTTALL, F.R.S. 
(From the Quick Laboratory, University of Cambridge.) 
(With Plate I.) 
CONTENTS. 
PAGE 
Introduction ..... .... 43 
I. Typhus fever and its conveyance by lice ... 44 
II. Relapsing fever and its conveyance by lice .... 57 
III. Miscellaneous infective diseases which lice may serve to spread . 66 
IV. Some other pathological effects attributed to lice ... 69 
V. Primary effects of louse infestation ..... 70 
VI. Note on the presence of anticoagulins in the salivary glands of 
P. humanus ......... 74 
Summary and Conclusions ....... 74 
Introduction. 
The following pages give an account of the part played by P. humanus 
in pathology, no summary of the kind having hitherto been published 
to the writer’s knowledge. Most attention is devoted to the part 
played by the louse in the etiology of typhus and relapsing fever because 
of their importance and prevalence in certain countries involved in 
the present war. The most important discoveries relating to these 
two diseases are of relatively recent date and this accounts, in a 
measure, for the ignorance of these achievements of science among many 
members of the medical juofession when the war began. As an 
example I may mention that after the war had lasted about a year, 
a physician of my acquaintance who was in charge of a large hospital 
actually scoffed at the statement that lice convey typhus and relapsing 
fever-—we trust that he has grown wiser in the interval. 
From the point of view of the historical sequence of the more recent 
discoveries bearing upon the two diseases mentioned, relapsing fever 
