464 L- R- CLEVELAND. 



6. Rats. 



The next logical step in the development of the work was to 

 oxygenate a warm-blooded vertebrate. Trichomonas (Tritricho- 

 monas in the opinion of some investigators) is present in a fairly 

 large number of rats; because of this, and owing to the ease with 

 which rats may be obtained, the rat was selected. In order to 

 demonstrate the presence of protozoa, fecal contents were re- 

 moved by means of a catheter, as in the experiments with frogs, 

 and were examined under the microscope. 



It was found, however, that the rats themselves were not able 

 to live more than five to six hours at 3.5 atmospheres of oxygen 

 and that their protozoa were not killed in this time. 



7. Trichomonas from Frog, Rat and Man in Culture. 



Since it w r as impossible to remove the protozoa from a warm- 

 blooded vertebrate by the method employed in removing them 

 from the cold-blooded vertebrate, the problem of the toxicity of 

 oxygen for the protozoa living in the intestines of rat and man was 

 attacked in another manner, viz. the protozoa were grown in 

 culture l and the cultures were oxygenated at 3.5 atmospheres by 

 placing a few drops of the fluid from each culture in the same flasks 

 that had been used in all the other experiments. 



It was found (see Table I.) that the Trichomonas of frogs was 

 killed in six hours, the Trichomonas of rats in ten hours, and the 

 Trichomonas of man in eleven hours. Obviously, it is impossible, 

 then, to kill the protozoa of the rat and of man by oxygenation at 

 this pressure without killing the hosts themselves first. 



It is interesting to note that the frog Trichomonas in culture is 

 killed in about one-half the time required to kill it in the frog. 

 This is perhaps explained in part by two facts: (i) oxygen is more 

 soluble in water than in blood, and (2) the host furnishes some 

 sort of resistance or barrier which makes it slightly more difficult 

 for the oxygen to reach the protozoa. 



1 Several of the culture media that have been employed by other investigators 

 were used, but the following medium, which is largely a compilation from utli< r 

 methods, was found to be very satisfactory. For frog Trichomonas, sodium citrate 

 I per cent, sodium chloride 0.5 per cent, Loffler's dehydrated beef serum 0.5 gram, 

 distilled water 100 cc.; for Trichomonas of man and rat, 0.2 per cent, more NaCl 

 was used. Growth was very abundant. Subcultures were made every three <l.i\ - 

 of the organisms from rat and man. The frog Trichomonas lived three months 

 sometimes without being transferred. 



