Soldo : Axenic Culture of Paramecium 



383 



derived from these animals are also particle free. It has not yet been possible 

 to rule out mutation as an explanation for this phenomenon. 



The existing synchronism between the particles and the host cell makes it 

 possible to quantitatively evaluate agents that may selectively inhibit the 

 particles themselves. Of interest here is the number of antibiotics that possess 

 this capability (table 2). ID50 values, derived in a manner previously de- 

 scribed/* reflect the relative effectiveness of these substances to inhibit particle 

 populations. This selective action correlates with the toxicity produced by 

 these agents in man. Antibiotics such as penicillin and tetracycline which 

 exhibit the least toxicity in man prove to be excellent particle inhibitors; those, 



Table 2 



A- Comparison of the Activity of Antibiotics in the X System 

 WITH Chronic Toxicity in Man* 



Antibiotic tested 



Actinomycin D 



Actidione 



Bacitracin 



Neomycin 



Polymyxin 



Candicidin 



Streptomycin 



Cephalosporin C 



Novobiocin 



Oleandomycin 



Chloramphenicol 



Aureomj'cin 



Terramycin 



Penicillin 



Tetracychne 



Toxicity in man 



Very high toxicity. 



Toxic — fatal to rats— 1 mg./kg. orally. 



Nephrotoxicity, proteinuria. 



Nephro- and ototoxicity. 



Causes renal damage. 



Toxic — used topically. 



Low toxicit} — damage to eighth cranial nerve on 

 prolonged therapy. 



Low toxicity — mice tolerate 5,000 mg./kg. intra- 

 venously. 



Low loxicit> — 7 mg./kg. intravenously tolerated 

 in man. 



Low toxicity — 40 mg./kg. orally tolerated in 

 children. 



Low toxicity — 30 mg./kg. tolerated in man. 



Low toxicity — 15-30 mg./kg. tolerated in man. 



Low toxicity — 15-30 mg./kg. tolerated in man. 



Verj' low toxicity — very well tolerated. 



Very low toxicity — very well tolerated. 



* Toxicity data obtained from Spector, W. S. 1957. "Handbook of Toxicology," vol. II. 

 t IDso ratios of greater than 1.2 indicate selective inhibition. 



such as actinomycin and neomycin produce varying degrees of toxicity in man 

 and are not selectively inhibitory for the particle. Thus, the particle-Pam- 

 mecium system might be useful in predicting chronic human toxicity of poten- 

 tially useful antibiotic substances. In figure 2 the effectiveness of penicillin 

 in reducing the X population is shown. Under the conditions of the experi- 

 ment complete destruction of the particles is achieved in 1 day at a concen- 

 tration of 100 units per milliliter of the antibiotic. 



Xutrilional requirements of X-beariiig Paramecium. A nutritional study was 

 made with particle-bearing and particle-free strains. The latter were obtained 

 by treating axenically cultivated, X-containing animals with penicillin to re- 

 move the particles. Both require a factor (or factors) present in a nondialyza- 

 ble aqueous extract of Baker's yeast. Chemical fractionation resulted in a 



