180 GARRISON AND LEYNES. 



miraeidia in a culture one hundred and sixty days (twenty-tliree weeks) 

 old. In cultures kept a longer time than this, we were nevei' able to 

 find anything but empty sliells or degenerated ova. 



Therefore it would appear that while the ova develop comparatively 

 uniformly until the miraeidia are, to all appearances, fully luature, the 

 escape of the miraeidia from their shells is, for a given number of ova, 

 a matter of considerable variation and that the hatching of the ova 

 thrown out in a single expectoration may be distributed throughout a 

 considerable period of time — according to our experience, seventeen 

 to eighteen weeks. This observation appears to explain the fact that we 

 have never been able to find a great number of free-swimming miraeidia 

 in our cultures at any one time, even though the sediment was very 

 heavily loaded with ova and it is possible that the gradual hatching of 

 the ova may prove to be not without significance when the complete 

 life-cycle of the parasite is known. 



Having determined the laboratory conditions under which development 

 of the ova of the lung-fluke was most favorable and observed the time 

 and manner of such development, the remaining experiments, with which 

 we are here concerned, were performed with the idea of ascertaining the 

 variations from these conditions under which development would still 

 take place. 



DEVELOPMENT UNDER VARIOUS CONDITIONS OF TEMPERATURE. 



Cultures placed in the incubator at body temperature (37° to 38° C.) 

 not only showed no development, but rapidly degenerated. Subjected 

 to such a temperature for ten days, the cellular content of the ova 

 appeared broken down into an amorphous mass of granules and, if re- 

 moved from the incubator, gave no evidence of development though kept 

 beside a control culture for several weeks. 



Cultures kept at room temperature until the miraeidia were developed 

 and then placed in the incubator at 37° gave similar results. Within an 

 hour the organisms became quiescent, although those on a control slide 

 were still actively motile. Within a few days they became broken down 

 into a mass of granular debris. 



The results of these two experiments would seem to be at least 

 presumptive arguments against the reported observation of partly de- 

 veloped ova in the tissues of the final host of the parasite (see Kellicott, 

 1894) and also against the possibility more recently suggested (see 

 Manson, 1908) that the miraeidia of Parago?iiniu,s might be the infecting 

 stage for man. 



Cultures kept in cold storage at from 11° to 15° C, 10° to 13° C, 

 and from 9° to 10° C. gave no signs of development after ten weeks, 

 but likewise no degeneration, and when removed from the cold storage to 

 room temperature, never failed to develop motik' miraeidia in about 



