On this medium Novy and McNeal have shown that T. lewisi and other trypanosomes multiply rapidly in the water of condensation, and that in many species subcultures can be carried on through an indefinite number of generations. Thus, T. gambiense has been cultivated for four generations; T. rhodesiense is much more difficult to cultivate. Unfortunately, T. gambiense is somewhat refractory and does not multiply readily in this culture medium. In such cultures, however, the trypanosome form may be lost, the flagellum springing directly from the anterior extremity and no undulating membrane developing. Cultivation is now utilized as a diagnostic method of demonstrating trypanosomes, if very scarce in the peripheral blood.
Interesting observations have been made by Laveran and others on a very striking phenomenon exhibited by trypanosomes, in certain circumstances, both in the blood and in artificial cultures. Upon the advent of unfavourable biological conditions in these media, such as the influx of sera of non - susceptible animals, increasing scarcity of nutriment (as in the alimentary tube of an appropriate invertebrate host), lowering of temperature, or the addition of chemical solutions to artificial cultures, the trypanosomes tend to congregate in bunches in which the posterior extremities of the parasites are apposed, the flagellated extremities remaining free (Fig. 44). One such group is termed a "primary" agglomeration, and may be composed of upwards of a hundred individuals. In many cases these primary clusters themselves become grouped together to form still larger tangled masses known as " secondary " agglomerations. Agglomeration does not of itself seem to have any ill effect on the constituent parasites, which may again disperse, apparently quite unaltered. Sometimes all the individuals forming a cluster become disagglomerated; at other times
water for twenty-four hours. After sterilization the agar is pipetted off into test-tubes and one-third volume of fresh rabbit's blood added. After sloping, the tube must be incubated to test sterility.
