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FLOATING EFFICIENCY OF LEVITATING MEDIA [ Vol. XXIV, Part IV,
4. That CuNO 3 solution had floated the highest number of oocysts on the
first centrifugations in seven out of the eight trials whereas ZnSO 4
solution succeeded only once to float greatest number of oocysts.
However, the means for the first centrifugations were not found to be
significantly different with the three solutions.
5. That the ratio of the mean number of oocysts recovered on the first
centrifugation to the mean ' primary recovery ' for a series of trials
was highest for brine (92 per cent) ; next in the order of merit were
ZnSO 4 (88 per cent) and CuNO 3 (87 per cent) solution respectively.
But here again these differences were not statistically significant.
6. That there was no statistically significant difference in subsequent recovery
of oocysts left by the three solutions used as primary medium and all
the subsequent recovery was affected in one centrifugation by the
first subsequent medium employed.
7. That all the three chemical solutions possessed fairly consistent floating
capacities. This fact was brought out when they were played a
number of times on different aliquots of the same material (vide
Table II).
It can be reasonably presumed that the fæcal suspensions contained a uniform
distribution of oocysts in them and that all the three solutions handled approximately
the same number of oocysts in each experiment.
The number of oocysts recovered by a chemical solution did not mean that all
the oocysts present in the sample were exhausted, but it only revealed that the
number of oocysts which this medium could maximally recover. A small number
of oocysts which the levitating medium failed to float to the top, were left suspended
somewhere in the column of the floating medium or stayed at the bottom. There-
fore, the number of oocysts that rose to the top truly reflected the floating efficiency
of a chemical solution.
Besides the significantly speedier recovery, and the numerical superiority
(though not a significant one) in the number of oocysts recovered, CuNO 3 solution
has got other advantages over the other two chemical solutions. Firstly, it does
not evaporate for long periods ; secondly, it does not crystallise thus making possible
prolonged observations, and lastly, it offers a cool and clear visual microscopical
field obviating eye strain.
Brine recovered greater mean percentage of oocysts (though not significantly so)
at first centrifugations. Nevertheless, it is cheap and readily available. Apparently,
it has floated more number of oocysts than ZnSO 4 solution though the difference
was not statistically significant. This observation differs from those of Faust,
et al., [1939] and Swartzwelder [1939] who found that ZnSO 4 solution was better
than brine to concentrate protozoal cysts in human fæces. Both of these media
crystallise very quickly under the coverslip thus the slides have to be examined
immediately after having been prepared.
All told, all the three chemical solutions are well-suited for recovering coccidial
oocysts both sporulated and unsporulated from fæcal suspensions. The slightly
higher cost of CuNO 3 is offset by a few definite advantages gained by its use. For
ordinary routine work brine is quite useful.