526 



PATHOGENIC MICROORGANISMS 



a classification of these organisms. They are apparently very numer- 

 ous and have been isolated from a great many different sources, both 



FIG. 109. BACILLUS XEROSIS. 



in connection with the human body and in nature. Recently Bunting 

 and Yates have claimed that an organism of this group has etiological 

 connection with Hodgkin's disease. Studies by many other workers, 

 notably by Bloomfield and Fox, and studies going on in our own 



laboratory show that organisms very 

 similar to these strains can be isola- 

 ted from the skin, from the lymph 

 nodes of healthy and diseased people, 

 from ascitic fluid in varying condi- 

 tions, and from supposedly sterile 

 tissues. They are frequently present 

 in the nasal mucus and in the throat, 

 and are so ubiquitous that any asso- 

 ciation of them with specific disease 

 must be very conservatively ap- 

 proached. 



Very similar to this group are the bacilli of pseudo-tuberculosis 

 ovis, isolated from necrotic lesions in the kidneys of sheep by Preisz 

 and Nocard. It is impossible at present to do more than indicate that 

 the ' ' diphtheroid bacilli" are a large heterogeneous group, held to- 

 gether by morphological and superficial cultural similarity and largely 

 consisting of saprophytes and probably harmless parasites on the hu- 

 man and animal body. 



Shick Reaction. The studies of Roemer and others have shown 

 that the blood of the majority of normal adults contains a small 

 amount of diphtheria antitoxin. This normal antitoxin probably ac- 

 counts for resistance of many individuals to diphtheria. Its presence 

 may be very easily detected by means of the Shick reaction. A stand- 

 ardized diphtheria toxin is diluted in normal saline so that 0.1 c.c. of 

 the solution contains 1/50 M.L.D. for a guinea-pig. This amount is 

 injected intracutaneously. If the blood of the subject has less than 

 1/30 unit of antitoxin per c.c., a positive reaction appears in twenty- 

 four to thirty -six hours, which consists in a slight infiltration of skin 



