Abstract
The amount of trypanocidal substance contained in a given solution is sometimes estimated in vitro by determining the degree to which the solution may be diluted before it ceases to immobilize the parasites.
For want of a better diluent, trypanosomes have usually been suspended in physiological salt solution (with or without the addition of citrate), although salt solution not infrequently immobilized the parasites in 30 to 60 minutes.
In 1910, the writer made observations which caused him to substitute serum for the salt solution he had previously employed in suspending T. brucei. Serum (when not bound by the medicament under investigation) had the following advantages:
1. The motility of the control parasites was greatly prolonged. This enabled the observations to be continued over a longer time.
2. The motility of the control parasites was accelerated. This enhanced the delicacy of the tests in vitro by rendering more striking the contrast between the poisoned and the non-poisoned trypanosomes.
It was found, moreover, that poisons not infrequently immobilized more quickly trypanosomes suspended in serum than they did those suspended in salt solution. This also seemed to give serum a slight advantage over salt solution as a medium in which to suspend trypanosomes.
Rabbit, ox, horse, goat, sheep, pig, chicken, rat, and mouse sera were tested and were found to be efficient in prolonging the motility of trypanosomes.
It soon became easy to keep on hand a large supply of serum, for experiment showed that cattle serum, filtered through a Berkefeld filter, bottled aseptically, and preserved in the ice-box, retained its activity for many months.
That the motility of trypanosomes is preserved longer in serum than in salt solution was noted years ago and has recently been emphasized by Schern, 1 but the writer is not aware that anyone has previously recommended suspending trypanosomes in serum for experiments in vitro.
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