THE MECHANISM OF AGGLUTINATION. 155 



not only against organized cells but against such chemical sub- 

 stances as have been recognized as coagulable. 



Experiment, indeed, justifies this supposition. If rabbits are 

 given several successive intraperitoneal injections of milk, pre- 

 viously heated to 65 degrees to sterilize it partially, after a proper 

 interval they give a serum that has specific properties against milk. 



A certain amount of this serum (for example 3 c.c.), is placed in 

 a tube and the same amount of normal rabbit serum is placed in 

 another tube. To each of these tubes milk is added (10 to 15 

 drops for example). The tube containing normal serum remains 

 opalescent and homogeneous. In the tube containing active 

 serum small particles rapidly appear that soon increase in size 

 and form thick flecks. The fluid then becomes separated into two 

 parts, one of which is quite limpid and the other of which con- 

 tains clumped masses which generally fall to the bottom of the 

 tube, leaving the clear fluid above. This sedimentation goes on 

 better if milk that contains little fat or, better still, milk that has 

 been passed two or three times through filter paper and so deprived 

 of part of its fat' globules, is used.* If milk containing a good deal 

 of fat is used, the clumps may float to the top carried up by the 

 fat corpuscles that they have enclosed. 



If these mixtures of milk with normal serum or with "lactoserum " 

 are passed through a filter paper, the latter mixture filters quite 

 clear without any of the whitish opacity which milk produces; the 

 mixture containing normal serum remains cloudy after filtration. 



Microscopical examinations of these mixtures of milk with sera 

 show that the lactoserum causes the formation of abundant granu- 

 lar masses that do not occur in mixtures with normal serum. This 

 granular precipitate resembles the clots of casein formed by rennin.f 



* The experiment is more striking if filtered milk of this sort is used. Such 

 milk does not stick to glass that it touches, and renders the fluid less opaque, so 

 that the agglutination may be more readily estimated. 



t We do not wish at all to assert that the agglutinin of lactoserum is identical in 

 action with rennin. There are distinct differences between these two substances. 

 The action of the agglutinin is much less dependent on a suitable temperature than 

 is rennin; as a matter of fact, it acts at a temperature so low that rennin is almost 

 inactive. Nor does our serum have the property of clotting relatively enormous 

 quantities of casein, as does rennin. Moreover, in a mixture containing a large 

 amount of normal serum and a small amount of milk, rennin has slightly, any 

 effect, whereas under these conditions agglutination appears on addition of 

 lactoserum. 



