UTILIZATION OF ANIMALS FOR BACTERIAL DIAGNOSIS 237 



diphtheria bacillus. The organism is readily distinguished by its 

 morphology with the methylene blue stain both from the nasal secre- 

 tion and from cultures upon Loffler's blood serum. When the nasal 

 secretion is profuse, as, for example, in acute or subacute coryza, 

 saprophytic bacteria, as Bacillus proteus, may develop in the nasal 

 secretion, causing extremely offensive odors. There is little evidence 

 that the organism is exciting inflammation, however; it would appear 

 that the secretion is a favorable medium for the development of the 

 organism. 



The virus of poliomyelitis may be found in the nasal secretion. Its 

 identification has been discussed above. 



THE UTILIZATION OF ANIMALS FOR BACTERIAL DIAGNOSIS 

 AND EXPERIMENTATION. 



Pasteur's brilliant animal experiments led Koch to formulate his 

 Postulates for the etiological relationship of bacteria to disease. A 

 rigorous demonstration of the etiological relationship of bacteria to 

 specific disease, said Koch, must fulfill the following conditions: 



1. A specific microorganism must be constantly associated with 

 the disease. 



2. The organism must be isolated from the lesion and cultivated 

 outside the body of the host. 



3. A pure culture of the organism must incite the disease when 

 introduced into a normal animal. 



4. The organism must be isolated from the experimental animal 

 again in pure culture. 



Experience has shown that many diseases of man cannot be exactly 

 reproduced in experimental animals and Koch's Postulates, therefore, 

 cannot be fulfilled with exactitude in these instances. Nevertheless, 

 experimental animals are indispensable both in diagnostic and 

 experimental bacteriological laboratories. They are used: 



1 . As culture media for certain types of bacteria which grow slowly 

 or feebly upon artificial media, particularly when the number of such 

 organisms is too small to permit of cultivation under artificial condi- 

 tions. The isolation of tubercle bacilli from urine, of glanders bacilli 

 from the lesions of glanders are illustrative. 



2. To obtain pure cultures of bacteria from mixtures, as the inocu- 

 lation of white mice with pneumonic sputum for the pneumococcus, 

 or rubbing mixtures containing plague bacilli upon the shaved abdo- 

 men of a guinea-pig to obtain pure cultures of B. pestis. 



