PROTEID PRECIPITINS. 



blood stains, or all kinds of prepared sausage so that the first and important 

 task is to obtain a clear solution. 



In dealing with blood, milk, or seminal stains, the parts of the clothing involved are 

 excised, divided into very minute shreds, and placed into a test-tube with a small amount 

 of 0.85 per cent, of salt solution. If the material is not too old, extraction of the above 

 nature, for one hour is usually sufficient, otherwise it may necessitate a period of twenty- 

 four hours or more. Stains upon solid material such as steel, wood, stone, etc., are care- 

 fully scraped off, and suspended in physiological salt solution. To obtain a clear solution 

 the extract must be passed through filter paper or eventually the lilliputian bacterial 

 filter. 



In the examination of meats, or other food stuffs, it is best to remove the 

 material for examination from the center of its thickest part, as this portion 

 has been least exposed to the methods of preservation, especially the high 

 temperatures. Three hours extraction is usually sufficient; the fresher the 

 meat., the shorter this period. Very much salted meats are best washed 

 with distilled water, previous to extraction. Inasmuch as a great deal of 

 fat interferes with the reaction it is advisable to remove it beforehand by 

 extraction wth ether and chloroform for twenty-four hours (Miessner 

 and Herbst). 



Before performing the actual test with the unknown blood stain, it is 

 best to try out the entire reaction with a similar but known blood stain in 

 order to make sure whether all the ingredients are in good working order. 

 In laboratories equipped for medico-legal examinations, stains made upon 

 linens from the blood of man, ox, pig, horse, etc., are always kept in readiness 

 for such preliminary tests. 



Uhlenhuth indicates a set of rules to be observed whenever the reaction 

 is undertaken. They are here cited in their original form, as practice has 

 shown them to be of great service. 



"In order to obtain sufficient extract for the test, a small amount of the material is 

 placed into a test-tube containing 5 c.c. of normal salt solution. This must not be shaken. 

 After one to two hours, 2 c.c. are poured off into another tube and gently shaken. If a 

 persisting froth appears upon the surface of the fluid, it can be taken as proof that suffi- 

 cient extraction has occurred, and the rest of the fluid is thereupon also transferred to 

 this tube. If no froth appears the 2 c.c. should be returned into the first test-tube and 

 the extraction continued until repeated tests finally show the presence of froth. It is 

 preferable not to disturb the sediment at the bottom of the test-tube. The extract even- 

 tually obtained may have to be filtered, if not absolutely clear. 



Such an extract is as a rule, stronger than that required for the test, i.e., i : 1000. If, 

 however, one drop of a 25 per cent, nitric acid solution is added to i c.c. of a i : 1000 

 serum dilution and then heated, a faint opalescence appears. Enough saline should 

 therefore be added to the final extract so that the nitric acid test corresponds to that 

 given by a dilution of i : 1000. 



The following mixtures are then made: 



