its Pathology ami Methods of Protective Inoculation. 295 



Preservation of the Virus. 



After having transmitted the disease through a succession of animals, 

 I found it possible to preserve its virulence unimpaired through a long 

 period of time. 



I bleed the animals into bottles which hold 800 c.c. of fluid. These 

 bottles are prepared by placing in them 50 c.c. of a 10 per 'cent, solu- 

 tion of neutral citrate of potash and plugging the necks with cotton 

 wool. Such bottles are sterilised in the autoclave previoiis to use. 

 After being filled with blood, the influence of the citrate arrests coagu- 

 lation, and the corpuscular matter soon subsides, leaving the more or 

 less clear plasma above. The latter is drawn off to half the original 

 bulk, and is replaced by a 50 per cent, solution of glycerine and water, 

 containing 0'25 per cent, of pure carbolic acid. Such a mixture 

 preserves its virulence quite unimpaired for over two years. One c.c. 

 of this material serves to induce the disease in its characteristic form, 

 but if the dose is increased to 3 or 5 c.c., the period of incubation is 

 shortened, and the post-mortem phenomena are less characteristic. 



From the observations I have made I have found that the subcu- 

 taneous injection of fresh or properly preserved horse-sickness blood 

 produces symptoms during life, and shows pathological changes after 

 death which are not to be distinguished from those found in the 

 spontaneously occurring cases of the lung form of the disease. It is 

 somewhat remarkable that the only cases in which I have succeeded in 

 producing the Dikkop form were those in which the virus which was 

 used was somewhat septic. - When, however, I have inoculated virulent 

 preserved blood into partially protected animals, I have in a number of 

 cases, although not in all, produced this form. In three cases where 

 the virus used has been sufficiently attenuated as not to produce death 

 but a longer febrile period than is found in the fatal cases, I have also 

 seen the Dikkop form produced. 



Effect of Desiccation on the Virus. 



Citrated blood dried in a thick layer was rendered non- virulent. 

 Where, however, such blood was rapidly dried on glass plates in very 

 thin layers it was found, whe,n 2 grammes was dissolved in salt solution 

 and injected into horses, that it produced fever, but not in a virulent 

 form. The fever thus induced gave practically no protection against a 

 dose of virulent blood at a subsequent date. Mild attacks of horse- 

 sickness do not, however, give such protection as is required to resist 

 virulent blood. 



