INFECTIOUS DISEASES. 579 



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

 the idea that feeding fodder and cereals poor in mineral salts and 

 gi-azing in pastures where the soil is poor in lime and phosphates will 

 cause the disease has been entirely disproved in many instances. 

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

 tism which is followed by an inflammatoiy condition of the bones, 

 terminating in osteoporosis. The idea that the disease is contagious 

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

 been isolated. Numerous experiments have been made by inoculating 

 the blood of an affected 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 

 horse, but without reproducing the disease. Petrone believes that the 

 Micrococcus nitriftcans causes osteomalacia 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 confirmed 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 

 two districts, in one of which the rainfall is 150 inches annually, 

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

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

 animals from the wet to the dry district is followed by immediate 

 improvement and frequently by recovery. In the wet district horses 

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

 no unfavorable or unhygienic surroundings produce the affection. As 

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

 indication of an acquired immunity 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 only, 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 ease by ticks 

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

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

 the microscope. 



On some farms and in some stables bighead is quite prevalent, a 

 number 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 years were 



