Annual Meeting 1127 



permeated with living bacteria and protozoa. It is supposed 

 that each of the many species has some duty to perform in 

 nature's economy. Bacteria are the universal scavengers. They 

 cause all organic matter to revert to its original elements, they 

 cause fermentation and store up nitrogen in the soil. Of the 

 many species of micro-organisms a few are able to multiply in 

 the tissues of the living animal body. Some of them do not seem 

 to exist naturally in nature outside of the animal body. Among 

 these are to be found the causes of the communicable diseases. 



As infectious diseases are the result of definite organisms 

 multiplying in the animal body the facts to be ascertained are as 

 follows: (1) How do these organisms gain entrance to the ani- 

 mal body, (2) when and how do they escape from the infected 

 animal, and (3) how long, and under what conditions, will the 

 specific organisms live outside of the animal body? Again, it 

 is important that the nature of the disease in the aifected animal 

 should be recognized, i. e., whether it is an acute general dis- 

 order or a localized affection. It is also desirable to appreciate 

 the variation in the form or manifestation of a given disease 

 under different conditions. The answers to these questions will 

 diifer for the various infectious diseases, so that to guide one 

 in the control of any given specific disease he must be in 

 possession of the required knowledge of its cause. 



The first and most important factor in the control of infectious 

 diseases seems to be knowledge of their cause and the means 

 for making an early diagnosis. Coupled with this must be a 

 knowledge of when in the course of the disease the virus is 

 eliminated from the infected. This is not so significant with the 

 highly infectious maladies where heroic measures are applied, 

 but with such diseases as glanders and tuberculosis it is very 

 important. All cattle that reacted to tuberculin were at first 

 considered immediately dangerous, but the researches of recent 

 years indicate that it is not until the disease process attains to 

 a certain stage that the specific bacteria are given off and the 

 animal becomes a menace to others. This fact is the crux of the 

 German method for controlling tuberculosis. It may not be 

 enough in itself but it takes us one step nearer the goal. 



The dissemination of viruses through secretions that may con- 



