CONTRIBUTIONS TO THE STUDY OF IMMUNITY. 53 



the trachea of cattle it was but a step to employ epithelial secretions 

 for the same purpose. In conjunction with this it was of considerable 

 theoretical interest to determine in this very way whether the specific 

 properties of cells are preserved in their secretion products. 



I have therefore employed milk for immunization and have first 

 treated guinea-pigs and rabbits with cow milk. The cow milk 

 immune serum thus obtained is able, so far as I have been able to 

 observe, to kill ciliated cells in the peritoneal cavity of rabbits, though 

 in a smaller measure than the specific ciliated epithelial immune serum. 



The affinities of an immune serum are readily determined when 

 the serum, like the ciliated epithelial immune serum for example, acts 

 also on red blood-cells, for then this can be used as a reagent. Cow 

 milk immune serum possesses the property to dissolve cattle blood 

 in a not inconsiderable degree. This haemolytic action, as in the 

 case of the blood immune serum and of the ciliated epithelial immune 

 serum, is due not to any increased content of complement but to the 

 presence of a specific immune body. Hence here also it was pos- 

 sible to compare the affinities of this immune body (for the ciliated 

 epithelium on the one hand and for the red blood-cells on the other) 

 with the affinities of the specific blood immune body. 



The two immune sera obtained by injecting rabbits with cow 

 milk and with cattle blood were therefore inactivated, equal quan- 

 tities of normal rabbit serum to serve as complement were added 

 to them in excess, and the mixture tested for its haemolytic properties 

 on cattle blood. The cow milk immune serum usually showed such a 

 degree of action that one part of the immune serum saturated with 

 complement was able to dissolve completely 20 parts of the custom- 

 ary 5% cattle blood mixture. 



Corresponding to this, therefore, the much stronger haemolytic 

 cattle blood immune serum was diluted with inactivated normal 

 rabbit serum or with physiological salt solution until, with an excess 

 of complement, the hsemolytic action of the two sera on cattle blood 

 was exactly equal. 



When the two immune bodies have in this way been made entirely 

 equal so far as the hsemolytic property is concerned, it is possible to 

 exactly compare their chemical affinities for a particular group of 

 cells. It is then easily demonstrated that the two hsemolytic immune 

 bodies differ in respect to their chemical relations to other cells of 

 the same species. 



Thus if equal quantities of ciliated epithelium are added to the 



