688 EXPEEIMENT STATION RECORD. 



growth taking place when the temperature ranges from 90 to 94°. At a tem- 

 perature of from 00 to 75° this may require 2 to 3 weelis. Only one molt was 

 observed, but from micrometer measurements it would appear that there are 

 two before the final molt in the free stage. When the free larvae become full- 

 grown they reach what may be called a pupal stage. Most of them secre*:e 

 a covering about themselves, inside of which the activities of the larva may bo 

 observed. This covering is called a sheath and when completed practically 

 seals the inclosed larva. The eusheathed worm is from 025 to 800 microns in 

 length and has the rear end elongated into a sharp point. . . . The length of 

 time the various stages of the worms may remain alive varies greatly with the 

 environment and probably with the individuality of eact worm to some 

 extent. . . . 



" In moist cultures in the open cages in the laboratory to which no water was 

 added, during the winter of 1908, the eusheathed worms were all dead after 

 a period of 93 days. Fresh material heavily infested, collected October 14, 

 1908, was put in cages outdoors after 85 per cent had eusheathed. The cages 

 were made of glass open at top and bottom to give as nearly out-of-door condi- 

 tions as possible. The maximum hatching occurred on October 29, 1908. The 

 eusheathed larvae attached to the glass wall of the breeding cage were ex- 

 amined at frequent intervals and after February 17 no live worms could be 

 found. ... It was particularly noticed that manure kept for 7 months in open 

 outdoor cages and which had to be soaked in water for some time before a 

 slide could be made for examination, contained more live, full-grown free worms 

 than the breeding cage walls." 



Young worms from infested feces which had been buried in sand to a depth 

 of 5 in. were found to come to the surface without any apparent obstruction, 

 and it is concluded that cultivation can not be depended upon to relieve 

 the situation under ordinary field conditions. It is thought that, as the 

 worms occur mostly in the mucous secretions between the ingesta and the 

 mucous membrane, their principal food consists of this mucus. The relation 

 of maximum infestation to the time of death or recovery of 20 animals studied 

 is shown in diagrammatic form from data obtained in 1908 by making daily 

 fecal examinations. It appears that the heaviest infestation occurred dur- 

 ing June and that another increase of infestation took place in some animals in 

 September. 



The seasonal and post-mortem records of .30 calves used in the experiments 

 in 1908 are also reported. In this study the author finds that " in case of two 

 calves of the same age on same pasture and giving about the same egg record, 

 one may die, the other survive. In case of two calves of same age on same 

 pasture, one having much higher egg record than the other, the animal with the 

 lower egg record may die while that with the higher egg record may not even 

 show symptoms of being affected by the infestation. In case of two calves, one 

 having a low egg record of short duration, the other a low, prolonged egg 

 record, the former may die, the latter survive." 



As young worm-free calves put on infested pasture show eggs in small 

 numbers in the feces in about 4 weeks, it appears that this is approximately 

 the time required for the young worms to complete their growth after they are 

 taken into the body. 



In reviewing the data relating to seasonal occurrence of injury at the 

 station, the author considers it evident that the percentage of death during a 

 single season is governed to a great extent by the amount of precipitation dur- 

 ing the main growing season, from June to September. The principal injury is 

 said to be done to spring calves. It is concluded that the intestinal parasites 

 are eliminated from the animal at approximately 14 months and sooner in 



