Hog Lung-Worms yagi 
TABLE 4. 
To Show the Rate of Growth of Metastrongylus apri in Millimeters, Attained Within the Soil. 
First WEEK Seconp WEEK 
Length Width Length Width 
~o2 015 42 O11 
.33 015 46 015 
.30 .012 40 .010 
sop 016 48 020 
31 014 .49 021 
.30 012 50 .025 
.29 : 011 42 O11 
.32 015 48 .020 
RY 012 .39 .018 
200 015 52 025 
THirD WEEK FourtH WEEK 
Length Width Length Width 
2a) 020 .63 028 
50 .018 nde, 037 
.60 035 74 054 
.65 .040 . 60 035 
50 018 67 025 
65 .035 .70 035 
.63 035 ie, 045 
.59 020 69 .035 
57 018 74 055 
.62 .032 .65 .040 
The above measurements are random selections of male and female larvae of both species. They at- 
tained their maximum size by the end of the fourth week, after which they began to die off. However they con- 
tinued to persist indefinitely. 
after they had been permitted to dry out in the soil at room temperature, 
by placing them in water. Incidentally it was noticed that many samples 
of these same larvae continued to live after they had remained in 
weak chloral hydrate solution for three months. Evidently, profound 
morphological changes occur during this time, which enable these para- 
sites to withstand unfavorable environmental conditions. 
Six weeks after this period of rapid growth, the larvae still re- 
mained active, but did not increase in size. Numerous cast skins and 
dead larvae began to appear. It is certain that moulting took place, 
but the actual number of these moults could not be determined. Un- 
favorable conditions seem to prolong the life cycle of these parasites, 
for they encyst and remain inactive, until such time as favorable con- 
ditions return. Apparently these larvae die off gradually if they do 
not find a suitable host. In the laboratory, they have persisted in this 
manner for almost a year. 
There are also good grounds for belief that these worms may 
develop directly within the lungs. Since, in a majority of cases, the 
initial lesion begins at the very posterior tip of the lung, and often 
contains great numbers of worms, the theory is hardly tenable that 
all these worms entered as individual larvae, and all migrated to this 
particular area of the lung. Most lesions that were examined, were 
found to contain these strongylus in all stages of development. The 
adult specimens lay massed together at the terminal end of a bronchus, 
while the more active larvae, equivalent in size to those which had 
