202 FAILURE OF BACTERICIDAL SERA 



immune body relatively both to the bacteria and to the com- 

 plement, and deviation of the latter may occur. Hence it is at 

 least conceivable that a dose of bactericidal serum may be 

 injurious in that it actually inhibits the normal bacteriolytic 

 processes that are at work in the blood-stream. We have already 

 quoted processes exactly parallel in describing the experimental 

 proof of the deviation of complement. 



Another suggestion that has been made is to use perfectly fresh 

 immune serum, or to reactivate it by fresh serum from a normal 

 animal. But this seems not to be successful, and apparently 

 alien complements rapidly unite with the tissues of the animals 

 into which they are injected, and so become inert. 



It would seem that no explanation based on deficiency in com- 

 plement will be found satisfactory : the facts concerning the 

 action of the dog's serum on anthrax bacilli appear to offer a 

 crucial experiment settling this point. Nor if the added ambo- 

 ceptor really acts as opsonin would the question of complement 

 come in. The most satisfactory explanation appears to be that 

 the sera do not actually come in contact with the bacteria in the 

 lesions, though they may, and very probably do, tend to sterilize 

 the blood, and so prevent further generalization of the infection. 

 This question of the accessibility of the bacteria in the lesions 

 to the substances circulating in the blood is probably one of prime 

 importance in immunity and recovery, and we shall meet with it 

 again in dealing with the opsonins. It seems to meet the facts 

 of the case very well with regard to the action of the serum in 

 dysentery. In acute cases it is of value ; and here the bacilli are 

 lying in regions which are fairly accessible to the blood. In chronic 

 dysentery it is almost useless, and in this form of the disease the 

 bacilli are shielded by a dense and impermeable layer of inflam- 

 matory tissues. And in cholera the bacilli are mostly lying in the 

 intestinal tract ; probably a few do gain access to the blood and 

 tissues, and are immediately destroyed. In typhoid fever the 

 bacilli are found in the blood early in the disease, and later, 

 roughly at the period at which antibodies make their appearance 

 in large amounts, they disappear. But there are always large 

 numbers in the lymph glands and spleen, regions in which it is 

 almost certain they are shielded from the action of the blood. 

 This explanation appears far more satisfactory than any depending 

 on deficiency in complement. 



If the bacteria in the blood-stream are actually dissolved by the 



