156 STUDIES IN IMMUNITY. 



Certain of these clumps are composed entirely of a fine granular 

 precipitate, and others enclose a large number of fat globules in 

 their midst. If a little more milk than can be agglutinated is added 

 to lactoserum, there is nevertheless an abundant deposit of the 

 agglutinated substance formed. After the deposition of all the 

 clumps, even to the smallest ones, the supernatant fluid is found to 

 be quite limpid. When taken off and mixed with normal serum 

 this supernatant fluid gives no opacity. If added to lactoserum, 

 however, it causes a slight cloud which soon increases and 

 is followed by flecks which form a considerable deposit. In other 

 words, the lactoserum has clumped casein that was in so fine a state 

 of division that it did not render the liquid turbid, and that had 

 escaped the agglutinating action of the first insufficient dose of 

 active serum. 



A similar experiment may be performed in the following manner: 

 as we have already stated, normal serum containing milk (for 

 example, 4 c.c. of serum to ten drops of milk) passes through filter 

 paper as an opaque fluid. If the filtration is repeated a number of 

 times through the same paper, a much clearer fluid, which is only 

 almost imperceptibly opalescent, is finally obtained. On micro- 

 scopic examination this fluid contains very few fat globules and 

 nothing else. If a small amount of this is mixed with equal parts 

 of normal serum, nothing happens. When mixed with lactoserum 

 in equal parts the fluid that was at first transparent immediately 

 becomes turbid, and rather voluminous white masses of casein 

 form, which, microscopically, are granular clumps, identical with 

 those formed by rennin. 



Similar precipitates may also be formed with whey produced 

 by adding rennin to milk. This whey when filtered is faintly 

 opalescent and causes no turbidity with normal serum; when added 

 to lactoserum it causes a very distinct turbidity which soon settles 

 down in the form of flecks. It is well known that whey still con- 

 tains casein which has escaped the effect of the rennin, but which 

 gives a voluminous precipitate on addition of an acid. 



*** 



Are there no analogies to be drawn between the appearance of 

 flaky precipitates in limpid fluids containing sufficient casein to 

 render them faintly opalescent when lactoserum is added, and the 



