180 EDWARD JENNER 



Thus far have I proceeded in an inquiry founded, as it 

 must appear, on the basis of experiment; in which, however, 

 conjecture has been occasionally admitted in order to present 

 to persons well situated for such discussions objects for a 

 more minute investigation. In the mean time I shall myself 

 continue to prosecute this inquiry, encouraged by the hope 

 of its becoming essentially beneficial to mankind. 



II 



FURTHER OBSERVATIONS ON THE VARIOLA VACCINE, OR 

 COW-POX. 1799 



ALTHOUGH it has not been in my power to extend the in- 

 quiry into the causes and effects of the variolse vaccinse much 

 beyond its original limits, yet, perceiving that it is begin- 

 ning to excite a general spirit of investigation, I think it of 

 importance, without delay, to communicate such facts as 

 have since occurred, and to point out the fallacious sources 

 from whence a disease imitative of the true variolae vac- 

 cinae might arise, with the view of preventing those who 

 may inoculate from producing a spurious disease; and, 

 further, to enforce the precaution suggested in the former 

 treatise on the subject, of subduing the inoculated pustule as 

 soon as it has sufficiently produced its influence on the con- 

 stitution. From a want of due discrimination of the real ex- 

 istence of the disease, either in the brute or in the human 

 subject, and also of that stage of it in which it is capable of 

 producing the change in the animal economy which renders 

 it unsusceptible of the contagion of the smallpox, unpleasant 

 consequences might ensue, the source of which, perhaps, 

 might not be suspected by one inexperienced in conducting 

 such experiments. 



My late publication contains a relation of most of the 

 facts which had come under my own inspection at the time 

 it was written, interspersed with some conjectural observa- 

 tions. Since then Dr. G. Pearson has established an inquiry 

 into the validity of my principal assertion, the result of which 

 cannot but be highly flattering to my feelings. It contains not 





