ESSAYS ON BACTERIOLOGY. 81 



the serum is in direct proportion to the quantity intro- 

 duced and to the degree of immunity previously con- 

 ferred upon the animal from which the serum was 

 obtained. 



The stage and intensity of the attack have much 

 influence upon the results obtained by this blood- 

 serum therapy. The longer the attack has lasted and 

 the more intense it is, the greater the quantity of 

 serum necessary to arrest its progress. This resist- 

 ance to the serum rises very rapidly, so rapidly, in- 

 deed, as to soon reach such a point as to require an 

 amount of serum impossible to introduce into the ani- 

 mal. Hence the desirability of progress in the direc- 

 tion of securing the immunizing or curative agent 

 from the serum in some more concentrated form. In 

 regard to the difficulty just referred to, it is less in 

 diphtheria than in tetanus. 



There are still many difficulties in the application 

 of- this serum therapy to the larger animals and to 

 man. Already considerable success seems to have 

 been reached in its application to human tetanus and 

 diphtheria, but it is yet too early to predict what the 

 outcome may be. The conditions in the labouatory 

 are quite different from those at the bedside, and we 

 must be careful how we carry over inferences and ex- 

 periments from one to the other. At present we can 

 but maintain an attitude of hopeful expectation, 

 strong in the conviction that sooner or la.ter every 

 gain in knowledge will result in practical good. 



