PNEUMONIA 147 



while others think that they only render phagocytic action more effec- 

 tive. The best pneumococci sera either in the fresh state or after 

 the addition of complement do not destroy the organism. They may 

 possibly stimulate the phagocytes or they may render the cocci more 

 susceptible to the phagocytes. In order to be of service either in 

 prevention or treatment, a relatively large amount of the immune 

 serum must be used. In other words, a certain degree of concentra- 

 tion must be reached. The law of multiple proportions which holds 

 good between diphtheria toxin and antitoxin fails here. Some have 

 found that the immune sera which they have studied are effective 

 only against those strains used in immunizing the animals and this 

 view has induced attempts to secure polyvalent sera, but up to 

 the present time these cannot be pronounced successful. 



Neufeld and Handel, in a discussion of the value of pneumococci 

 sera, conclude that experiments on animals have shown that such 

 have not only a protective but a curative effect on both septicemic 

 processes and pneumonia, but not until the dose is large enough to 

 reach a certain concentration in the body. 



Some of the strongest opponents of the phagocytic theory admit 

 that natural immunity to this disease is due to phagocytic action and 

 that extracellular destruction of the pneumococcus has not been dem- 

 onstrated. Furthermore, they state that even normal serum in large 

 doses protects animals against this infection. 



Inasmuch as a large proportion of healthy people carry the pneumo- 

 coccus in their mouths and throats, the question of what happens when 

 one develops the disease, becomes one of both practical and scientific 

 interest. Several possibilities suggest themselves. In the first place, 

 while this organism is found in most cases of lobar pneumonia, it is 

 not found in all instances. Moreover, while frequently present in 

 other forms of pneumonia, it is not so constantly present in these. 

 The best of evidence exists for the statement that true croupous 

 pneumonia may be due to other bacteria, such as the pneumobacillus, 

 Streptococcus pyogenes and Streptococcus mucosus. These facts have 

 led some to believe that pneumonia may be due to the conjoint activity 

 of two or more organisms, but no two of these are constantly found 

 and there seems to be no substantial basis for this idea. A second 

 possibility is that the pneumococcus normally present in the saliva 



