INFECTIOUS DISK.\SKS. 57i> 



more or less plausible; but none of thtiu has been established. Thus 

 the Idea tliat feedin*^: fodder and ceieals poor in niiniMal salts and 

 gra/.in«>j in i)asturos where the soil is poor in lime and phosphates will 

 lause the disease has been entirely ilisproveil in many instances. 

 Others have considered that the disease starts as a muscular rheuma- 

 tisui w liiiii is followed by an inflammatory condition of the bones, 

 terminating in osteoporosis. The idea that the disease is contagious 

 has been advanced by numy writers, although no causative agent has 

 l>een isolated. Numerous experiments h:i\e been nuide by inoculating 

 the blood of an atfected horse into normal horses without results. A 

 piece of bone taken by Pearson from the diseased lower jaw of a colt 

 was transplantetd into a cavity made for it in the jaw of a normal 

 hoi*se, but without reproducing the disease. Petione believes that the 

 Microrocrufi lu'frip'cann causes osteomahu-ia in man as a result of its 

 producing nitrous acid, which dissolves the calcareous tissues, and 

 when injected into dogs in pure culture a similar disease is produced. 

 It is probable that if this work is confirmod a somewhat similar causa- 

 tive factor will be discovered for osteoporosis. 



Elliott considers the latter disease to be of microbic origin, the 

 result of climatic conditions, and divides the island of Hawaii into 

 tw«> districts, in one of which the rainfall is l.'iO inches annually, 

 where bighead is very prevalent, and the second of which is dry an<l 

 rarely visited by rain, where the disease is unknown. Kemoval of 

 ^inimals from the wet to the dry district is followed by inunetliate 

 improvement and frequently by recovery. In the wet district hor.ses 

 in both good and bad stables take the disease, but in the dry districts 

 no unfavorable or uniiygienic surroundings produce the aliection. As 

 both native and imported horses are equally susceptible, there is no 

 indication of an acquired imnumity to be observed. 



Theiler has recently stated that his experiments in transfusing 

 blood from diseased to normal horses were negative, and has sug- 

 gested that the causative agent may be transmitted by an interme- 

 diate host oidy, as in the case of Texas fever. He draws attention to 

 this method of spreading East African coast fever, although blood 

 inoculations, as in osteoporosis, are always without result. We know 

 that coast fever is infectious, and that it can not be transmitted by 

 blood inoculations, but is conveyed with remarkable ea.se by ticks 

 from diseased cattle. That the cause has not been observed may lie 

 accounted for by its being invisible even to the high magnification of 

 the microscope. 



On some farms and in s<^)me stables bighead is (|uite |)revalent. a 

 nunjber of cases following one after another. On one farm of Thor- 

 oughbreds in Pennsylvania all the yearling colts and some of the 

 aged horses were affected during one year, and on a similar farm 

 in Virginia a large proportion of the horses for several vears were 



