Hog Lung-Worms 269 
gators, namely, that older hogs or pigs are more resistant to these 
worms. If we omit these digressions, our curve will then show a 
decided symmetry. March was found to be the month of least in- 
fection, and this is doubtless due to their getting rid of parasites 
during the winter months, and not acquiring. subsequent infection. The 
dotted line represents a period during which no observations were 
made. Again, the maximum infestation is found to occur during the 
summer and fall months. The percent of affected hogs diminishes 
gradually during the winter months, until it again reaches the lowest 
level in March. In the succeeding months of April and May, a rather 
sharp rise may be noted, and this in a measure corresponds to the warm 
rainy weather of these two months. It would seem therefore, that 
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CHART FOR TABLE LI. 
