26 BOAED OF AGRICULTURE. 



it goes on to pathology and therapeutics ; and we have never 

 intended to drop our investigations with the demonstration of 

 the germ theory, but we hope to push them forward until all 

 the problems which I have referred to are solved, and perhaps 

 others which may arise as the work progresses. We have 

 confidence in patient, persevering work when properly di- 

 rected, confidence in the scientific methods of the present day, 

 and we feel certain that these researches will be continued 

 until the most difiicult and obscure questions connected with 

 contagious diseases have received a satisfactory solution. 



Now, as a sort of recapitulation of what I have been trying 

 in my imperfect way to say to you, I would add that we 

 have not the slightest doubt as to the correctness of the 

 germ theory of disease. Not only can the germs of many ani- 

 mal plagues be easily seen and cultivated, but their identity 

 with the active principle in the virus can be established be- 

 yond a doubt. Take, for example, the virus of fowl cholera, 

 and if you heat it to 132° for fifteen minutes, you at once 

 and completely destroy its activity ; and it requires just ex- 

 actly the same length of time and the same temperature to 

 destroy the germs which exist in this virus. A single degree 

 less for the same length of time leaves the germs capable of 

 multiplication, and the virus capable of producing the dis- 

 ease. And so the virus is rendered inactive by precisely the 

 proportion of carbolic acid, or sulphuric acid, or chloride of 

 zinc, or iodine, or other disinfectant, which is necessary in a 

 given time to kill the germs. The disappearance of life in 

 the germ and activity in the virus at the same time and under 

 the same conditions might in a single instance pass for a re- 

 markable coincidence ; but such remarkable coincidences are 

 not found so regularly in nature that they can be interpreted 

 in any other way than the identity of the germ and the essen- 

 tial agent in the virus. 



The attenuation of the virus of certain diseases and the im- 

 portance of the new methods of vaccination are also accepted 

 as fixed facts. But the situation in America is much difier- 

 ent from what it is in France. There one of the most fatal 

 and prevalent diseases is malignant anthrax, and the virus of 

 this happens to be the one of all others best suited for vacci- 

 nation purposes, because of its peculiarity of forming spores. 



