VII. QUICK-FREEZING AND FREEZING-DRYING 227 



wide scale. One of the earliest applications of freeze-drying was in 

 the control of rinderpest (cattle plague) in Africa. The mortality for 

 this disease is high, sometimes reaching 50 to 75%. In preparation 

 of the virus the blood of infected animals is laked and centrifuged. 

 This separates the leucocytes with which the live virus is associated. 

 Without drying, the virus remains viable and effective as an immuniz- 

 ing agent for a matter of a few weeks only. However, it survives 

 freeze-drjdng well and has its life extended to months and years. 

 Cattle are immunized by the simultaneous inoculation of living virus 

 and immune serum, this being similar to the practice of immunizing 

 swine against hog cholera. 



The viral vaccine for prevention of canine distemper has been pro- 

 duced in a small way commercially. Various fowl viruses are pro- 

 duced by desiccation. Vaccine for the prevention of yellow fever in 

 man has been successfully produced on a rather large scale. In ex- 

 perimental work the virus of influenza has been freeze-dried. Vaccine 

 for intradermal injection for immunizing against smallpox by Jenner- 

 ian prophylaxis (10) has all been distributed after freeze-drying. 

 There is some question about the efficacy of this method of immuniza- 

 tion but this has no bearing on freeze-drying per se (being related to 

 the nature of the material itself and the method of carrying out im- 

 munization) . 



Munce and Reichel (14) have shown that hog cholera virus of blood 

 origin, when desiccated under high vacuum and stored in vacuo in 

 flame-sealed ampules, remained infective after exposure to a tempera- 

 ture of 60°C. for 96 hours. At 37°, the infectivity was maintained 

 for 328 days. PhenoHzed liquid virus from the same mixture was 

 noninfective after exposure to the higher temperature for only five 

 hours. At 37° the period of infectivity of the dried preparation was 

 approximately 23 times as long as for the phenolized liciuid virus. 

 After storage at 20°, the dried virus was still infective in the authors' 

 last test, which was conducted after a storage period of 1125 days — 

 12 times as long as for the corresponding phenolized liquid virus. It 

 may be pointed out that hog cholera virus, as commercially available, 

 consists of the phenohzed, defibrinated blood of artificially infected 

 swine undergoing an attack of acute hog cholera at the time their 

 virus-laden blood is collected. This virus preparation is freciuently 

 referred to as "simultaneous hog cholera virus" because it is used 

 simultaneously with anti-hog cholera serum in the immunization of 

 swine against hog cholera. The animals would not survive the injec- 



