68 THE DEFENSIVE FORCES OF THE MACROORGANISM 



seems to stand to reason. We may imagine that in infections of 

 sufficient magnitude the normal opsonins are immediately used up 

 to a greater or less extent, and that their new formation as well as 

 the production of specific tropins then begins. We know but little, 

 however, of the mechanism by which this is brought about, and by 

 which the quantity to be produced is regulated, not to speak of the 

 origin of the bodies in question. As far as the latter point is con- 

 cerned, some observations which I made, together with Lamar, led 

 us to look upon the leukocytes themselves as the possible source 

 of the opsonins, but the evidence was not conclusive. On the other 

 hand there can be but little doubt that the production of opsonins 

 and tropins is caused in consequence of the absorption of bacterial 

 products. This phase of the subject has been thoroughly investi- 

 gated by Wright and his pupils, who found that the injection of 

 killed cultures (vaccines) of various bacteria will increase the opsonic 

 content, if employed in suitable amount, whereas overdoses will 

 cause a diminution. 



This observation throws light upon the remarkable fluctuations 

 in the opsonic content of the blood that have been noted by many 

 observers during the course of various bacterial diseases. We may 

 well imagine that these fluctuations are brought about by irregular 

 absorption of bacterial products, and it naturally suggests itself that 

 in those diseases particularly which are characterized by a certain 

 chronicity, and in which the opsonic content tends to be low (tuber- 

 culosis, acne, furunculosis, gonorrheal arthritis, etc.), it might be 

 possible to raise the latter by artificial means (vaccination) and thus 

 to influence the infection in a favorable way. This assumption, how- 

 ever, presupposes that an increased content of normal opsonins or 

 the appearance of specific tropins would be the only factor lacking 

 to insure adequate phagocytosis and thus an eradication of the infect- 

 ing organisms; but, as I have already mentioned, there is evidence 

 to show that with virulent bacteria at least, in which the virulence 

 is due to capsule formation, phagocytosis may not take place even 

 though opsonins or tropins be present in abundance, and it is indeed 

 possible that this factor may be responsible for some of the unsatis- 

 factory results which vaccination has thus far yielded in the curative 

 treatment of bacterial diseases. 



