RESISTANCE TO INFECTIOUS DISEASE 19 



disease and subsequently have had their immunity intensified by in- 

 jections of highly virulent blood, the cattle so vaccinated will develop 

 rinderpest in a mild form and will subsequently on recovery be also 

 immune; and yet during the process of immunization their blood con- 

 tains highly virulent parasites so that if a little of it be introduced 

 into non-protected and healthy cattle, they will be given rinderpest and 

 will die of it. 



The reaction of the body to the bacterial vaccines injected is out 

 of proportion to the quantity of culture introduced. Thus two milli- 

 grams oi dead cholera bacilli injected under the skin of human beings 

 will yield enough of the specific immunity substance for these bacilli to 

 bring about the destruction of 60,000 or more milligrams of the culture. 

 There can be, therefore, no direct transformation of the cholera bacilli 

 into immunity bodies, but they must exert a stimulus on certain cell- 

 functions through which the immunity principles are produced ; and 

 the quantity of their formation depends not on the weight of crude 

 bacilli introduced, but on the strength of the stimulus impressed upon 

 the sensitive cells to which they react in a specific and remarkable 

 manner. 



Is it possible in the course of an established infection to reinforce 

 the resistance of the body? I have already stated that it is not prac- 

 ticable to bring out at the height of an infection an efficient heightened 

 reaction of physiological resistance; but from this it does not follow 

 that under these conditions a special form of immunity reaction may 

 not be elicited. The tuberculin reaction, or that part of it which is 

 specific, may be cited as an example of this kind of reinforcement ; and 

 whatever there is of value in the treatment of infectious diseases by 

 means of dead cultures of their specific bacteria — " vaccines " so-called 

 — must be of the nature of an intensified immunity reaction. What 

 is sought to be accomplished in the latter case is the formation in cer- 

 tain uninfected localities — in the subcutaneous tissues, for example — 

 of immunity principles that afterwards by escaping into the blood 

 shall assist in the termination of an infectious process situated else- 

 where in the body. Such local foci of immunity as it is designed to 

 create in the subcutaneous tissue are not unknown. The pleura can be 

 given a local immunity to the typhoid bacilli; the subcutaneous tissue 

 to tetanus toxin, and it is highly probable that the normal resistances 

 exhibited by our mucous membranes to the pathogenic bacteria they 

 harbor are examples of such local immunities. 



I fear that I have carried you far afield and into somewhat devious 

 paths of immunity to disease. You will, I know, not complain and hold 

 it to the detriment of medical science, that these paths have not been 

 already converted into fine open roads. But you will prefer to recall 

 how brief is the time since where the paths now are there were only 

 wood and tangle. 



