IXFLL'E.XCE OF CLl.MATE ON ANIMAL DISEASE. 497 



F. to 50° F. this time may var_y from a coui)le of weeks to a few 

 hours. 



The effect of temperature is further noted in examining- the 

 rate of development from the egg to the infective larval stage. 

 According to Ransom, the rate of their development at different 

 temperatures is as follows: — At a constant temperature of 05 " F. 

 this period occupied three to four days; at 70° F., six to 14 days 

 were occupied ; whilst from 46° F. to 57° F. the time occupied 

 may be from three to four weeks. 



The im])ortance of moisture Ransom refers to in dealing 

 \\-ith the hnal infective larval stage, for here he jioints out that 

 *' it is only when moisture is supplied that these larvae can crawl 

 up the blades of grass from which they gain access to their 

 host." Even here, however, he states temperature is again an 

 important factor, since below 40° F. he found the larv?e to show 

 little or no activity. Provided, however, tliat the temperature is 

 suitable, these larv?e, he says, crawl u]) the grass blades during 

 wet weather and dewy nights, ceasing their migrations when the 

 humidity of the atmosphere falls below saturation point or when 

 the dew evaporates. Their movements, he further says, resume 

 or cease according to the presence or absence of moisture, and 

 thus they moiuit higher and higher up the grass glades, propor- 

 tionately increasing their chances of bein.g consmned by a host. 



The importance, however, of actual collections of water such 

 as pools he regards as being indirect rather than direct, in ]xjint- 

 ing out that the larvcC tend to fall to the bottom of these, and will 

 only be ingested if sheep in drinking stir up the mud from the 

 bottom of such pools. He believes that the chief importance such 

 pools possess is in keeping the earth surrounding them moist, 

 and at the same time raising the humidity of the air in their 

 neighbourhood. 



Observations made in regard to the effects of the reverse 

 conditions of coldness and dryness are as follows :- — Drying, he 

 states, speedily kills the eggs and immature embryos, and a 24- 

 hours' freezing may prove fatal in a number of cases. On the 

 other hand, the sheathed infective larval stage is, according to 

 Ransom, very resistant to drying and freezing. Thus he men- 

 tions that this form resisted drying for 35 days in fseces, and 

 that, placed out of doors for a continuous period of 85 days, they 

 were still alive at the end of th.is time, although for 494 hours 

 of this period the temperature was 30° F. lower, the larv:^ 

 being thawed out 32 times and remaining continually frozen for 

 over 48 hours on three different occasions. 



Coming next to the observations made by \>glia in .South 

 Africa,* we may note some of his results in the same way, and 

 the more important to us are the following: — 



* These results, obtained by Dr. Ve.glia. liave not as yet Iseen published, 

 but will sliortly appear in the Report of the Director of Veterinary Re- 

 search. The remarks made here refer to information verbally communi- 

 cated to the writer for the purposes of this article througli the kindness of 

 Dr. VeRlia. 



D 



