Hog Lung-Worms PAL 
numbers that they practically filled up the stomachs and intestines of 
all affected individuals. Superficial diagnosis should therefore be al- 
ways followed by a post-mortem or microscopic examination. 
The typical appearance of a lung affected with these parasites will 
show the initial lesions occurring at the very posterior tip. These lesions 
are gray in color, and have a solid appearance and feeling. A sharp 
demarkation also exists between the healthy and affected portions. These 
last rise prominently against the general surface, and are due to the 
clogging up of air tubes by the bodies of the worms and the debris they 
produce. Adult worms feed on blood and lymph by puncturing the 
walls of blood vessels, thus causing an acute inflammation. The eggs 
and larvae produce a diffuse pneumonia characterized by a dry puffiness 
of lung tissue. In old hogs, extensive, watery tumors occur, in which 
remnants of dead worms can be found. Small nodules, very charac- 
teristic of true tubercles, are also present. 
One noticeable feature of these examinations was the common 
occurrence of bacterial lesions associated with the presence of these 
parasites. Probably these worms do not carry infection themselves, but 
the watery tumors which they produce undoubtedly make excellent cul- 
ture media for any bacteria that chance to find their way into the lungs. 
In the hundreds of cases that were examined, secondary infections of 
this nature were of frequent occurrence. Lung-worms. may thus be an 
important factor in causing disease. 
Lire HISsTory. 
The general paucity of exact information in the field of parasitology 
is made very apparent when we attempt to find some concrete state- 
ments regarding the parasite in question. Until quite recently, nothing 
was known of its life history. The following report, copied from Cali- 
fornia Experiment Station circular 148, presents our most authentic 
knowledge of this subject. 
“Early in our investigations we observed that the embryos found 
in the lungs were of two kinds. Our first thought was that these might be 
embryos of two different species of lung-worms, but this was discounted 
by the fact that we could find but one species of adults in the lungs. 
That the difference might be due to sex was rejected owing to the fact 
that the types differed not only in shape and structure, but also in 
their movements, location and habits. Thus the theory gained belief 
that these two types were designed to maintain a free-living and a 
parasitic generation. This belief was confirmed by Doctor von Linden 
of the University of Bonn, who found that in the mucus of the trachea 
and of the space behind the nose there were slim, strong-moving em- 
bryos that were capable of living outside the body. In the lungs the 
embryos were short, thick, slow moving and unable to live outside the 
body. Dr. von Linden found that if slim, strongly moving larvae are 
placed on moistened earth they continue their development, and she 
has been able to raise eleven successive free-living generations in this 
way. 
“Dr. von Linden believes that the embryos destined to reproduce 
the free-living generations, work their way up to the trachea and are 
