372 DISEASES OF CATTLE, SHEEP, GOATS, ETC. 



hour. At a temperature ranging from 48 to 60 F. forty-one days 

 are required for the eggs to hatch. The life history and habite of 

 the worm have been studied by Conradi and Barnett. 



Upon hatching, the young hook worms are very minute, but 

 can easily be seen with the aid of a hand lens when crawling on 

 the glass walls of the breeding jars. They have a tendency to con- 

 gregate, and these clusters can be easily recognized with the un- 

 aided eye. In this stage, as well as in the egg stage, they are very 

 susceptible to heat or cold, being easily killed. Drought is also 

 fatal, the worms dying in a few minutes. They feed on the fecal 

 matter about them. In the second stage they are but slightly har- 

 dier. After several days the body wall becomes thicker and more 

 rigid, and soon they pass to the final larval stage. 



The larvae that were hatched from eggs, gathered from fresh 

 feces on February 26, and hatched February 28, had mostly passed 

 to the final larval stage on March 15. In this stage thej^ are pro- 

 tected by a resistant covering called "sheath." Worms kept in the 

 laboratory during January and February, the temperature varying 

 from 48 to 60 F., passed to the final larval stage in forty-one days. 

 While active they were able to continue feeding through the aper- 

 ture in the front end of the sheath. They move up and down on 

 any; near-by moist object, whether it is earth, grass, leaves, or 

 weeds. They finally become quiescent in some elevated position, 

 discontinue feeding, and are men greatly resistant to heat, cold, 

 and drought. This habit of rising appears to be advantageous, as, 

 we believe, the principal method of host infestation is through the 

 mouth. 



That part of the life history from egg to larval stage is very 

 probably completed in a few days during the warm weather of 

 summer. 



The eggs and young worms require moisture. It seems quite 

 probable that little development takes place in feces dropped on a 

 hill during the drought of summer. There is said to be little 

 danger from infestation in running water. 



At present the outlook for a cure for this disease is not very 

 encouraging. Thymol has given good results in the treatment of 

 the disease in man, and has been recommended by some author- 

 ities for the disease in cattle and sheep, but we believe it is far from 

 being a specific. Certainly, in the case above referred to, with a 

 dose of 150 grains, it could not be noticed that the worms had been 

 in the least affected three days later. However, further experi- 

 ments with this drug will be made as opportunity presents itself. 

 Even if drugs such as thymol were effective in expelling worms, 

 the animal, if still pasturing on infested land, would continue to 

 reinfest itself, so that the problem resolves itself into a question of 

 prevention rather than treatment, the outlook for which is more 

 encouraging. 



When it is remembered that the disease occurs chiefly, or al- 

 together, on low, wet lands, and that in dry seasons it is less severe, 

 it would appear that much could be done by avoiding such places 



