ON FILTRATION OF SERUM COMPLEMENT 93 



retained on account of their size. This is made sufficiently 

 evident by the permeability which appears after a time 

 (vide infra). In speaking of complement being fixed by the 

 filter, we mean that it apparently combines with its sub- 

 stance, and is thereafter not recoverable. For example, if 

 after filtering fresh serum, some salt solution is passed 

 through the filter, this does not carry the retained comple- 

 ment with it, and if then the filter be pounded in a 

 mortar and treated with salt solution, no complement is 

 obtained in the fluid. We have hitherto failed by any 

 means to recover complement after it has been removed by 

 the filter. As various particulate substances have the 

 property of absorbing complement, we tested the effect of 

 adding the powdered substance of the filter to fresh serum, 

 and shaking the mixture thoroughly. Practically no absorp- 

 tion of complement by the substance of the filter can be 

 shown in this way. Accordingly the passage of the serum 

 through the pores of the filter seems essential to the pheno- 

 menon. 



The following experiments show that the property 

 possessed by a filter of stopping complement is soon lost in 

 the process of filtration. Such experiments have all been 

 performed on the same plan. A quantity of serum, usually 

 about 4 c.c. diluted with an equal quantity of salt solution, 

 is filtered ; the filter is then washed thoroughly by passing 

 water through it in the reverse direction ; it is then thoroughly 

 dried at 57 C., and its properties are again tested by filtering 

 a fresh amount of serum. The following are illustrative 

 examples : 



EXAMPLE 1. Dose of complement before filtration . 0-005 c.c. 



after filtration . 0-25 



The filter is then washed and its properties are tested, with the 

 result : 



Dose of complement before filtration .... 0-005 c.c. 

 after filtration . 0-015 , 



