PREVENTIVE MEDICINE 325 



and indeed before the act of parturition had even commenced. So 

 far preventive measures embracing all the supposed predisposing 

 causes have not given much success. 



SCRAPIE. 



This disease of sheep is most frequently associated with intense 

 irritability of the skin, and sometimes nervous symptoms. In Great 

 Britain at the present time it appears to be enzootic in the extreme 

 north of England and south of Scotland, though the same disease 

 has also been described in parts of Germany and France. Scrapie 

 has been investigated during recent years by M'Fadyean, Stockman 

 and others, and though light has been shed upon many points regard- 

 ing the occurrence of the disease there are still many questions which 

 will only be solved by patient research. Though essentially a dis- 

 ease of sheep, it has been alleged to occur in goats. According to 

 Stockman, it was probably first brought to England in the latter part 

 of the eighteenth century by Merino sheep imported from Spain or 

 Saxony, and for a time existed in Norfolk, from which county it 

 spread towards the north. Within the regions in which scrapie 

 at present exists the disease is probably somewhat irregularly dis- 

 tributed, and it occurs especially among the large flocks kept on 

 hill pastures. Probably no breed of sheep is insusceptible. It is 

 seldom seen in animals under 18 months of age, no doubt owing 

 to its extremely long period of incubation, but adult sheep of any 

 age may be attacked. It seems most commonly to occur among 

 2 year old ewes, and frequently at about the lambing season. 

 The course of the disease is somewhat chronic, cases usually lasting 

 about 3 or 4 months, and few animals appear to recover. Accord- 

 ing to Stockman the common percentage of loss in infected flocks 

 is 4 per cent, per annum, though it may be higher. Many different 

 theories as to the cause have been brought forward. M'Gowan 

 considers scrapie to be due to sarcosporidia, but the evidence is 

 meagre in the extreme, and at the present moment the etiology is 

 most obscure. Though it seems likely that the disease is a micro- 

 parasitic one and is spread by contagion, no one has yet been able to 

 transmit it either by experimental inoculation or by contact, or to 

 demonstrate the existence of the virus. The possibility should be 

 noted that infection may occur in lambs before birth as well as after. 

 In M'Fadyean's experiments out of 11 lambs born of infected ewes 

 only 2 developed scrapie. Stockman has recorded cases in which 

 the disease has been introduced into healthy flocks by rams from an 

 infected flock. 



