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BULLETIlsr 1369, U. S. DEPARTMENT OF AGEICULTUEE 



In the writers' experience they have found that grubs may be ex- 

 tracted at any time during the course of their development in the 

 backs of the cattle. They have found that, by removing the small 

 scabs which usually develop aroimd the apertures cut by the young 

 or third-stage larv£e, they can be pressed out with great ease. There 

 seems to be a period in the fourth stage during which extraction is 

 more difiioult. By using care, however, practically every grub can 

 be removed by hand. (Fig. 36.) 



Fig. 36., — Extracting Hypoderma lai'va from cow by pressing down around cyst 



opening 



Tliere is a very marked difference in the ease with which grubs 

 may be etxracted from the backs of cattle of different breeds. In 

 the case of the island breeds the skin appears more flexible and 

 elastic, and extraction is comparatively easy. Very often with the 

 Holstein-Friesian and certain beef breeds it is almost impossible to 

 squeeze the grubs out by hand. The condition of flesh of the host 

 also' has a considerable effect on the ease of extraction. Very poor 

 or extremely fat cattle are more difficult to treat than those in fair 

 condition. 



The method of procedure in extracting grubs may be modified to 

 suit the individual and also the character of the skin of the host 

 under treatment. Inexperienced people often find extraction ex- 

 tremely difficult ; but those who have considerable experience are able 

 to remove the grubs with comparative ease, and they seldom break 



