56 INFECTION AND RESISTANCE 



the dark, may give positive reactions even after years, as experi- 

 ments by Uhlenhuth have shown. Meyer 29 claims even to have 

 obtained a precipitation with extracts of the material of mummies. 

 One of his specimens was a mummy dating back to the first Egyptian 

 Empire (5,000 years), the other about 2,000 years old. Pieces of 

 the leg and neck muscles of these specimens were chopped up finely, 

 extracted for 24 hours with salt solution, then filtered until clear. 

 With antihuman serum they gave turbidity after one hour at 

 37.5 C. 



Under conditions of putrefaction, of course, the precipitinogen 

 is more rapidly destroyed, though blood putrefies with surprising 

 slowness, even if, as in our own experiments, the conditions of mois- 

 ture, temperature, and reinoculation with putrefactive bacteria are 

 constantly observed. Under such conditions a weak reaction may be 

 obtained after as long as a month or six weeks. 



In carrying out the tests with any material it is first necessary 

 to get it into clear solution, a result which is best accomplished by 

 soaking it in a small quantity of isotonic salt solution. Preliminary 

 to this it is always necessary to scrape off a bit of the specimen and 

 examine it microscopically to discover, if possible, whether blood cells, 

 sperm, or other cellular constituents can be detected. The infusion in 

 salt solution should be continued for several hours if necessary for 

 12 to 24 hours. After the first few hours in the incubator the material 

 should be placed at room or refrigerator temperature so that the 

 yield in unchanged protein may not be diminished by the action of 

 bacterial growth. After extraction the solution may be filtered in 

 order to clear it, but often mere centrifugation suffices for this pur- 

 pose. The concentration of antigen in such an extract is always an 

 uncertainty, but may be determined with sufficient accuracy for 

 practical purposes by shaking and observing the formation of a 

 lasting foam. Protein solutions will show foam on shaking in dilu- 

 tions as high as 1 to 1,000, and if the original amount of salt solution 

 used, in washing out the material is properly gauged to the amount 

 of blood available in the stain, and the solution shaken and observed 

 for the formation of foam, it is usually a simple matter to obtain a 

 final concentration approximating one to one thousand. 30 



The antiserum which is used should be of such a potency that 

 preliminary titration with the specific antigen, diluted 1 to 1,000, 

 should give an almost immediate cloudiness at room temperature. 



By testing this serum against a number of other varieties of 



2 9 Meyer. Munch, med. Woch., Vol. 51, No. 15, 1904. 



30 If there is enough material, .the amount of dissolved protein can be 

 also approximately gauged by adding to a little of it a drop of acid, boiling 

 and observing the. heaviness of the cloud which forms. A control test of a 

 known dilution of the suspected variety of blood can be made at the same 

 time and the heaviness of this cloud compared with that in the test solution, 



