An account is given of the coprophilic habits of the holotrichous ciliate, Balantiophorus minutus Schew., and of the effect upon it of urine.
Experiments are described in which attempts were made to grow the ciliate in a wide range of human faeces of varying consistency and from both normal and diseased subjects. Abundant growth was obtained in normal faeces, both before and after dilution; but no growth took place in the undiluted faeces of softer or liquid consistency from various cases of intestinal disorder, even dilution frequently failing to render these a suitable medium. Moreover, the ciliate could not be recovered from such abnormal faeces by subculturing.
This behaviour was due to two primary factors:
(1) the high osmotic pressure obtaining in liquid stools which causes plasmolysis of the ciliates, and (2) the presence in the stools of unaltered bile salts, owing to the rapid passage of material through the intestinal tract. It was demonstrated that bile salts, even in very low concentrations, are highly toxic to B. minutus. Two secondary factors probably also serve to limit growth, namely, the presence of drugs with a toxic or depressing effect on the ciliate, and the presence of urine, which is not only highly lethal but also mixes more readily with a liquid than with a normal stool.
It was shown that the lethal action of urine upon the ciliate was due primarily to osmotic pressure, and, to a lesser degree, to the toxic effect of ammonia sometimes present in the urine. It was demonstrated that a concentration of urine as low as 5% inhibited multiplication in ordinary cultures, while as little as 1% prevented growth when admixed with normal faeces. It was further shown that urea has a depressing effect upon the reproduction of B. minutus. Paramecium caudatum was shown to be also susceptible to the lethal effect of urine.
Investigation of the effect of hypertonic solutions has shown that the limiting osmotic pressure which B. minutus can withstand for a prolonged period is represented by a solution of non-electrolyte with a depression of the freezing-point of about 0·60° C., or by a solution of an electrolyte with a depression of the freezing-point of 1·2° C. (represented by 1·9% sodium chloride solution) which is equivalent to about 6000 mm. Hg (8 atmospheres). It was also shown that osmotic pressure is not the principal limiting factor to the growth of the ciliates in such stools. The ability of other ciliates to live in hypertonic solutions is discussed and the conclusion is reached that B. minutus is more resistant than is usual among freshwater forms.
Experiments carried out on mice established that the cysts were incapable of passing through the mammalian alimentary tract and developing in the faeces after passage, so proving that B. minutus is an exogenous coprozoon.
It is concluded that (i) only polysaprobic Protozoa capable of movements in a viscous medium can lead an existence in undiluted faeces; (ii) under natural conditions urine probably acts as a limiting factor to the development of coprozoic ciliates in faeces; (iii) coprozoic Protozoa are derived from the soil fauna and have in turn largely contributed to the sewage fauna.
