252 STUDIES IN IMMUNITY. 



lactalbumin from cow milk. These experiments with the various 

 milk derivatives have been frequently repeated and always with 

 the same result. 



We obtained milk casein by the well-known method of diluting 

 with three volumes of water and precipitating with 0.1 to 0.2 per 

 cent acetic acid. The resultant precipitate is redissolved with 

 ammonia, 1 to 200, and reprecipitated twice with acetic acid. 



The casein purified in this manner is dissolved in water, rendered 

 alkaline with ammonia and made equal in amount to the original 

 volume of the milk; neutralization is then made with phosphoric 

 acid. 



The lactoglobulin and the lactalbumin were obtained from whey 

 by the same method employed for dog serum. They were all 

 finally redissolved in a much smaller amount of fluid than the 

 original whey volume. We know from Bordet's studies that in 

 order to produce complete fixation of alexin by bacteria and spe- 

 cific serum that a considerable number of bacteria are necessary. 

 Since lactoglobulin and lactalbumin are present in such small 

 amounts in milk we should not expect them, in absence of casein, 

 which forms the bulk of organic substances, to fix all the alexin in 

 the presence of rabbit > milk serum. 



With these substances prepared in this way three identical series 

 of tubes are prepared corresponding to those in the experiment 

 with rabbit > milk serum and whole milk. In addition to a fourth 

 control series of milk and rabbit > milk serum there are the three 

 other series containing casein, lactoglobulin, and lactalbumin 

 respectively in place of whole milk. 



In the tubes of each series that contain normal rabbit serum, 56 

 degrees plus each of the substances in turn, hemolysis is complete; 

 the alexin is not fixed by any of these substances without rabbit > 

 milk serum. But in the mixtures of milk or milk derivatives and 

 specific serum, hemolysis occurs only in the mixture containing 

 lactalbumin, and is lacking in the tubes containing casein and 

 lactoglobulin as well as in the one with whole milk. In other words, 

 alexin is fixed by rabbit > milk serum with both casein and lacto- 

 globulin; it is not fixed, however, with lactalbumin. We may add 

 that the precipitating property of the serum parallels the sensitizing 

 property; we obtain a distinct precipitate by adding casein or lacto- 

 globulin to the specific serum, whereas the addition of lactalbumin 



