CAUSES OF THE EVOLUTION AND EXTINCTION OF THE TITANOTHERES 



871 



immune to the disease and are said to be "salted," 

 but horses that have recovered from the disease con- 

 tinue to act as reservoirs and remain sources of infec- 

 tion throughout their lives. 



The same is true of Piroplasma canis among the 

 Carnivora spread by the dog tick {Haemophysalis 

 leachii). The blood of recovered animals remains 

 infective. 



EPmEBncs 



Epidemics in North America. — We are indebted to 

 Thompson Seton (1909.1) for bringing together a 

 large number of observations recorded by many 

 authors on epidemics among the American mammals. 

 In the summer of 1873 a fatal epidemic is said to have 

 destroyed three-fourths to nine-tenths of the prong- 

 horn antelopes (Antilocapra) in the area between Yel- 

 lowstone and Missouri Rivers in Montana (Allen). 

 An epizootic distemper called black tongue killed 

 thousands of white-tailed deer in Texas in 1856 

 (Walton). Tuberculosis broke out among the New 

 England deer in 1901, destroying chiefly the older 

 ones (Murch). A species of distemper killed off vast 

 numbers of the beaver of upper Red Deer River, 

 Alberta, about the year 1800, and they have never 

 been so plentiful in that region and eastward to Hudson 

 Bay since that year (Tanner). In western Manitoba 

 the wonderful "rabbit year," 1886, in which these 

 animals are said to have multiplied to the number of 

 5,000 to the square mile, was followed in the ensuing 

 winter by a destructive plague due to a staphylococcus 

 which may have started in some skin wound or para- 

 sitic skin disease (Little); from a condition of extra- 

 ordinary abundance the rabbits practically disap- 

 peared. According to Hornaday a parasite, the 

 bloodsucking stomach worm (Strongylus strigosus), 

 may have caused the so-called seven-year plague 

 among northern varying hares (Lepus variabilis) and 

 the rabbits of the West. Seton observes that the 

 great periodic decrease in the lynx, which in every 10 

 years or so reduces their number to about one-tenth 

 of the maximum, is probably due indirectly to the 

 periodic rabbit plagues — that is, to starvation through 

 failure of the rabbit supply. Many emaciated bodies 

 of the lynx are found in such seasons. 



Epidemics in Europe. — Fleming, in his "Animal 

 plagues" (1871.1), enumerates eighty-six epidemics 

 that affect wild quadrupeds and birds. In the list 

 are diseases that affect nearly every wild species in 

 Europe and some in the New World, including the 

 red deer {Cervus elapJius), the reindeer (Rangijer 

 tarandus), the chamois (Rupicapra tragus), and the 

 wild hog; also, among the Carnivora, wolves, foxes, 

 and bears; among the Rodentia, hares, rabbits, and 

 rats. Various forms of tuberculosis account for a 

 large percentage of death among domesticated ani- 

 mals. Among animal plagues anthrax was formerly 

 the most rapid and deadly, but it is now perhaps the 



least common, owing to Pasteur's discoveries. Amer- 

 ican zoologists are familiar with the spread of disease 

 from domesticated to nondomesticated animals — of 

 the sheep scab, for instance, to the wild sheep {Ovis 

 montana). 



The feline and ursine Carnivora are protected by 

 their relatively nongregarious habits ; canids are highly 

 gregarious and consequently would be more subject 

 to the spread of eipdemics. On the contrary, the 

 gregarious Herbivora offer favorable conditions for the 

 spread of disease. 



Epidemics in Africa. — In his "Great Rift Valley" 

 Gregory (1896.1, pp. 265-266) observes that the great 

 herds of game which roamed over the steppes of South 

 Africa are being rapidly decreased. Man no doubt 

 has played the leading part in the annihilation of the 

 enormous herds that once thronged Cape Colony. The 

 fact that during the last few years the game has re- 

 treated from the Somali coast into the interior shows 

 how easily it can be driven from a district. In South 

 Africa, however, man's work of extermination has 

 probably been insignificant as compared with that of 

 natural agencies, such as lions and disease. Vast 

 herds of the wild buft'alo {Bubalus ca.-ffer) were exter- 

 minated between 1890 and 1893 by the cattle disease 

 (rinderpest), which also killed off the gnu and giraffe. 

 Gumming (1855.1, vol. 1, p. 138) observed as early as 

 1855 that 



the goat in many districts is subject to a disease called by the 

 Boers "brunt sickta," or burnt sickness, owing to the animals 

 afflicted with it exhibiting the appearance of having been burnt. 

 It is incurable, and if the animals afflicted are not speedily killed, 

 or put out of the way, the contagion rapidly spreads, and it is not 

 uncommon for a farmer to lose his entire flock with it. This 

 sad distemper also extends itself to the ferae naturae. I have 

 shot hartebeests, black wildebeests, blesbucks, and springbucks, 

 with their bodies covered with this disease. I have known 

 seasons when the three latter animals were so generally affected 

 by it that the vast plains throughout which thej' are found were 

 covered with hundreds of skulls and skeletons of those that had 

 died therefrom. 



Howorth observes (1887.1, p. 174): 



Frequenters of the forest with whom I have conversed, 

 whether Europeans or Singhalese, are consistent in their assur- 

 ances that thej' have never found the remains of an elephant 

 which had died a natural death. One chief, the Wannyah of the 

 Trincomalee district, told a friend of mine that once after a 

 severe murrain, which had swept the province, he found the 

 carcasses of elephants that had died of disease. 



Entozoa in elepJiants. — Several specimens of the 

 African elephant (Loxodon africanus Blumenbach) 

 were autopsied by MacCallum (1907.1). Little has 

 been written about the Entozoa of this species, 

 which apparently differ in many respects from the 

 better-known forms infecting Elephas indicus. 



It is said that elephants succumb to the infestation 

 of parasites more than from any other cause, and the 

 worm that most often destroys these animals is a 

 species of ParampMstomum. Members of this genus 



