24 TSE ETIOLOGY OF THE BACTERIAL DISEASES. 



formed within the bacterial cells readily diffuses through the cell 

 walls and enters the circulation, while the organism itself is confined 

 to relatively a small area and may not be found in the blood at all. 

 Such diseases are properly called bacterial intoxications. In some 

 other infectious diseases, such as anthrax and one form of the plague, 

 the germ itself may be distributed by the blood and lymph to every 

 part of the body ; these diseases are designated as septicemias. 



With the proof established that the deleterious effects wrought by 

 germs are due to chemical poisons elaborated by them, let us infi[uire 

 what properties a microorganism must possess before it can be said 

 to be the spedjio cause of a disease. The four rules of Koch have 

 been conceded to be sufficient to show that a given germ is the sole 

 and efficient cause of the disease with which that germ is associated. 

 Briefly these rules are as follows : 



1. The germ must be present in all cases of that disease. 



2. It must be isolated from other organisms and from all other 

 matter found with it in the diseased animal. 



3. The germs thus freed from all other foreign matter must, when 

 properly introduced, produce the disease in healthy animals. 



4. The microorganism must be found properly distributed in the 

 animal in which the disease has been induced. 



We will briefly discuss the applicability of these rules. When it 

 is stated that the germ must be present in all cases of the disease, it 

 need not be understood that an unlimited number of cases must be 

 examined before the causal relation of a given organism to the disease 

 may be reasonably suspected. This would require more than a life- 

 time, and would demand facilities for the study of the special disease 

 that do not and cannot exist. The number of cases in which the germ 

 is constantly found should be reasonably large, and the larger this 

 number the greater the probability that the organism is etiologically 

 related to the disease. Moreover, the germ may be present in all 

 cases, and yet it may not be found in all. To demand that it be 

 found in all cases would be to presume that the methods of detecting 

 and recognizing a given organism are perfect, and there is no ground 

 for this assumption. Again, since the results of no one man's work 

 can be accepted in science until they have been confirmed by others, 

 the personal equation must be considered; what one man finds, 

 another may fail to find. Diligence, skill and accuracy are not 

 equally developed in all men, and, moreover, the methods employed 

 may differ. To illustrate these points : Koch, after the most pains- 

 taking study embracing twenty-nine cases of pulmonary tuberculosis, 

 nineteen of miliary tuberculosis, twenty-one of tuberculous glands, 

 thirteen of tuberculous joints, ten of tuberculosis of the bones, four 

 of lupus, and seventeen of bovine tuberculosis, announced that he 

 had discovered a bacillus which is constantly present in tubercular 

 disease. Since this announcement thousands of physicians and bac- 



