W. Nicoll 
381 
review of the Nematode parasites of rodents, a subject which has acquired 
extraneous medical interest as a result of Fibiger’s investigation on rat cancer. 
Ascaris lumbricoides has formed the subject of a fairly important work on 
chemical physiology by von Kemnitz, but this is of little intrinsic interest to 
helminthologists. 
At the present time the life-history and mode of development of parasitic 
worms are most important subjects of research and discussion both from a 
zoological and from a medical point of view. The complicated life history of 
some of these worms is at times baffling and requires much patience and per¬ 
sistence in its elucidation. 
Without doubt, during the past decade several discoveries of the very 
highest importance have been made. Chief amongst these must be placed the 
work on Bilharziasis. This subject has called forth a greater bulk of literature 
than any other in Helminthology. Ten years ago we owed a large part of our 
knowledge and opinion on the subject to Looss but he, curiously enough, formed 
the conclusion, based apparently on negative observations and experiments, 
that no intermediate host was concerned in the life-history of Bilharzia 
{Schistosoma) haematobia and that the larval parasite after its escaj^e from 
the eggshell was able to re-infect the human subject in the miracidial or first 
larval stage by direct penetration through the skin. Such a conclusion was, 
needless to say, opposed to all previously acquired ideas of the life-history of 
digenetic Trematodes though the fact that the Schistosomes are so sharply 
differentiated structurally from all other digenetic Trematodes lent colour to 
the supposition that their life-cycle might also be radically different. The 
subject, however, was of such great economic and medical importance that 
this conclusion could not be accepted without very much more definite and 
irrefutable evidence. Such evidence has been accumulatively forthcoming 
from various quarters, particularly Japan and Egypt. 
It is impossible, in a brief summary, to enter into full details of this volu¬ 
minous work. A recent review of current knowledge and progress in the 
matter has been written by Fairley (1919) but the most comprehensive 
account is contained in Leiper’s original reports on the work of the Bilharzia 
mission in Egypt (1915-1918). This report will probably take rank as the 
greatest helminthological classic since Looss’s monograph on Ancylostoma. 
Though it be true that some of Leiper’s results were forestalled by Japanese in¬ 
vestigators ( e.y . Miyairi and Suzuki, 1914) and that he may be indebted to them 
for suggestive ideas, yet the credit of the completed work is undoubtedly to 
a large extent his. It has been shown definitely that an intermediate molluscan 
host plays a necessary part in the life-cycle of the parasite. The important 
feature remains, however, that infection can take place through the intact 
skin. The chief point for consideration is the interpolation of the intermediate 
host for, from a prophylactic point of view, this affords a useful if not par¬ 
ticularly vulnerable point of attack in the life-cycle. Further reference will 
be made to this. 
Parasitology xiv 
25 
