The Inspissation Method 391 



out destruction of virulence, in from twenty-four to thirty-six hours. 

 The material thus dried is like chalk and easily pulverized. It 

 is, however, highly hygroscopic and if permitted to absorb water 

 becomes leathery and loses virulence rapidly. 



In a later paper Harris* found that the more thoroughly and 

 rapidly' the material is frozen, the greater will be the amount of 

 virulence remaining after desiccation. A new method suggested 

 is as follows: 



The brain or cord is ground in a porcelain mortar, with the addition of 

 water drop by drop until a thick smooth paste is formed. Carbon dioxide snow 

 is then collected from a tank in the ordinary manner and is added in small 

 amounts to the paste which should be stirred thoroughly meanwhile to prevent 

 the material freezing in 3 solid mass. Freezing occurs rapidly and when complete 

 the material is very brittle and easily reducible to a fine powder. During the 

 pulverization more snow is added from time to time to prevent thawing. When 

 the material is thoroughly pulverized, it is transferred to a small beaker with an 

 excess of snow and placed in the bottom of a Schubler's vacuum jar which has 

 previously been half immersed in a mixture of salt and ice and become thoroughly 

 cold. A beaker of sulphuric acid is then placed on wire gauze in the upper part 

 of the jar in such manner that there is free access of air between the frozen material 

 and the sulphuric acid. The acid is placed in the upper part because if placed 

 below, it soon freezes at the low temperature. The vacuum should measure 

 less than 2 mm. of mercury. During desiccation the temperatures should not 

 be allowed to rise above — is°C. The jar should be rotated gently several 

 times daily to mix the water and the acid. A single brain will become thoroughly 

 dry in from thirty-six to forty-eight hours. 



The object in thoroughly pulverizing the virus is two-fold. It 

 results in a inore complete mixture, so that all parts contain an equal 

 amotmt of virulence. Secondly, it permits of more rapid drying 

 and an easy transfer into smaller containers for subsequent tests. 

 To avoid any absorption of moisture, the dry powder is transferred 

 from the beaker to smaU glass tubes the ends of which are sealed in 

 a flame. The transfer is effected in a moisture-free atmosphere by 

 coveriag the top of the beaker with rubber dam held in place by ad- 

 hesive strips. A small puncture is made in the rubber large enough 

 to admit the tube, and through this the tubes are inserted and fiUed. 

 From 20 to 100 mg. is a convenient amount put into each tube. If 

 the tube has a diameter of 4 mm., each millimeter of powder will 

 weigh approximately 2 mg. 



Harris beUeves that the use of desiccated virus in an ti-rabic im- 

 munization of animals and persons offers many advantages over 

 other methods. 



Harrist reports that 182 patients have been injected with the 

 virus thus prepared for the purpose of immunizing them against 

 hydrophobia. No deaths have occurred and no compHcations de- 

 veloped. It is thus to all appearances a safe and efficient method 

 and is especially economical to the laboratory in time,, labor and 

 money." Material can be prepared two or three times a year and 

 put aside in the cold to be used only when needed and as one rabbit 



* "Jour, of Infectious Diseases," igi2, x, 369. 

 f'Jour. of Infectious Diseases," 1913, xiii, iss- 



