4<J^ INFLUKNCE OF CLIMATE ()N ANIMAL DISEASE. 



animals. Sucli a possibility, however, also remains a matter for 

 ftu'ther research to prove or disprove. 



All of these facts, then, showin.t,^ how favourable our sub- 

 tropical climate is to the existence of tick and insect-borne dis- 

 eases, it is satisfactory to be able to ])oint to one example of a 

 pest against which our climate seems to |)rotect us, and this is to 

 be found in the condition due to the ])resence in the subcutaneous 

 tissues of cattle of the larvcC of the " warble liy." 



In Euroi)e and A.merica the jjresence of the larva? of the 

 ■■ warl:)le fly " ( 1 1 \podcnna bovis or Hypodcniia liucata) in the 

 sulxmtaneous tissue of affected cattle offers a very serious eco- 

 nomic jtroblem by reason of the dama.^ed condition of the hides 

 ])repared from the skins of affected animals. In South Africa, 

 however, the "' warble fly " larvee have not so far in any authen- 

 ticated case been observerl to be i)resent in cattle born and bred 

 in tliis country, nor, so far as the writer is aware, has the adult 

 fly been met with, and the interest of this observation becomes 

 apparent vrhen we remember that the larvae of the fly have been 

 repeatedh' introduced into this countr\' in affected cattle im]-)orted 

 from oversea countries. 



This woifld seem to indicate that climatic and local con- 

 ditions are in some way unsuited to the jnipation of the insect 

 in this country. The exact explanation still remains a matter 

 for ftirther work to supply, but it is possible tliat dryness may 

 perhaps then Ije fou.nd to play an imi)ortant i)art in this con- 

 nection. 



Here now, however, let us leave the consideration of these 

 tick and insect-borne diseases, and ])ass to the next i^rou]) of 

 diseases to be dealt with. 



Diseases dui-: to Helminthic PAl^\slTES. 



In considering- this group two diseases may be taken to serve 

 as examjiles illustrating the ]:)oints which it is desired to make 

 evident. One of these exam])les is a form of distomatosis due to a 

 parasite of the grou]) of flatworms or Platyhielminthes. whilst 

 the other is a form of strongylosis caused by a ])arasitic worm of 

 the Xematode grotip. 



In considering these exami:>les, we will hrst deal with the 

 conditions due to the iilatyhelminthic parasite, and the particular 

 form of distomatosis to which we shall refer is that caused by 

 the presence of the j^arasite known for a long time as Disfoiiiinn 

 licpaticiini. now more correctly referred to as Fasc'wla hcpatica, 

 and ])opularl}- known as tlie " liver fluke " or sim])ly " fluke." 



This parasite Fasc'wla hcpatica is one which is met with in 

 more than one animal species, but is perhaixs best known as a 

 parasite of the bile-dttcts of the sheep, and the disease caused by 

 it in this case has been recognised all over the world — as, for 

 example, in Europe, North and South America, Australia, Japan, 

 China. India, Africa, North as well as South, and in other ])laces 

 as well — as, for instance, the Sandwich Islands. It is thus a 

 ver\- interesting" disease frf)m the point of view of distribution. 



