274 E VOL UTION AND DISEASE. 



seen that the form of idiocy known as cretinism is 

 recognized in calves, dogs, and lambs. Horses are cer- 

 tainly known to suffer attacks of acute mania, and dogs 

 become demented and are occasionally imbecile, not 

 recognizing their master from other persons, and forgetting 

 their own names. From being keen at sport, they fail to 

 recognize a hare or partridge, even blunder over them in 

 a field and take no notice of the game when it rises. 

 Convulsions caused by troubles during dentition are well 

 recognized in dogs, as well as a nerve affection, closely 

 similar to epilepsy. The remarkable affection of human 

 beings termed locomotor ataxy, and the singular St. 

 Vitus' dance, or chorea, occur in dogs. 



It will, perhaps, be desirable to conclude this chapter 

 by a brief consideration of the strange disease known as 

 Elephantiasis arabtMn^ the zoological and geographical 

 distribution of which is limited in an interesting manner 

 by mosquitoes. 



In India, China, Egypt, Arabia, the West Indies, and 

 Australia this disease is endemic : it is characterized by 

 enlargement of the parts affected, which may be the 

 arms, legs, and other parts of the body. The skin cover- 

 ing the part becomes enormously thickened, forms hard 

 masses and folds obscuring the toes when the legs are 

 affected, producing an appearance not unlike an 

 elephant's leg. One of the most remarkable features in 

 this extraordinary disease is that very frequently the 

 blood of individuals with elephantiasis swarms with 

 minute haematozoa, named by Lewis Filaria sanguinis 

 hominis ; and recent researches go to show that the 

 presence of filaria in the blood in association with 



