president's address. 869 



blood of a diseased fowl, conclusive evidence that the organism 

 was the cause of the disease. The growth of this organism 

 occasions no putrefaction in the liquid, so that this is an example 

 of a bacterium which is most destructive as a disease ; but which 

 at the same time, is entirely destitute of septic property. After 

 this bacterium has grown for a certain time in a portion of 

 chicken broth it ceases to develop further, and the broth is found 

 to have lost only a small proportion of its substance by weight, 

 has not undergone putrefaction, and still continues an excellent 

 pabulum for other forms of bacteria, yet the bacterium of the 

 fowl cholera (so called), though introduced from some new source, 

 is incapable of growing in it. 



This fact seems highly suggestive of an analogy with the effects 

 of vaccination or those of an attack of measles, scarlatina, &c, in 

 securing immunity from the disease for the future. Here we 

 have a certain medium invaded by a virus capable of self -multi- 

 plication, as is the case with those diseases in the animal body ; 

 the medium itself little affected chemically by the growth of the 

 virus within it, but nevertheless rendered unfit for the develop- 

 ment of that virus for the future. But something more than the 

 suggestion of analogy with vaccination has been effected by M. 

 Pasteur. By cultivating this bacterium in a particular manner 

 he enfeebles the organism and produces such an alteration in it 

 that when inoculated into a healthy fowl it produces only a 

 modified and no longer a fatal form of the complaint, but the 

 fowl is thereby rendered secure against taking the ordinary form 

 of the disease. It has been really vaccinated, if we adopt M. 

 Pasteur's extension of the term vaccination to other similar cases ; 

 but though the vaccination with the modified bacteria of the fowl- 

 cholera dees not occasion the fatal disease, it produces pretty 

 severe local effects. 



Professor Liston mentions other important experiments which 

 have proved successful in preventing contracting a disease in its 

 fatal form. Cattle have been inoculated with the blood of a 



