418 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1952 



cause vestibular and auditory pathology when given over long periods. 

 The polypetide antibiotics possess somewhat more toxicity. Tyro- 

 thricin and its constituents gramicidin and tyrocidine have a systemic 

 toxicity that precludes their parenteral use or makes their application 

 into body cavities and other sites where absorption is likely unde- 

 sirable. Bacitracin is nephrotoxic and its parenteral use is justified 

 only under exceptional circumstances. The broad-spectrum anti- 

 biotics, aureomycin, chloramphenicol, and terramycin are essentially 

 nontoxic but they may give rise to sensitization reactions and are apt 

 to induce minor gastrointestinal disturbances. 



As one would expect, the presently employed antibiotics are readily 

 absorbed following one or more standard routes of administration, 

 are able to diffuse into the various tissues, are considerably more active 

 against the parasitic cells than against the host cells and, once their 

 work has been completed, they are destroyed by normal metabolic 

 processes or are excreted from the body by natural routes. 



Many of the other antibiotics are of no clinical value because of 

 their adverse pharmacological activity. These substances, although 

 highly bacteriostatic, are either too toxic for use in man or are slowly 

 absorbed, poorly diffusible, or inactive in the body. These properties 

 can only be determined after thorough pharmacological study and 

 serve to emphasize the importance of pharmacological techniques in 

 the final evaluation of any new antibiotic. 



