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 
grazing 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 inflammatory 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. Pétrone believes that the 
Micrococcus nitrificans 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 
accounted 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 
