222 H. M. WOODCOCK. 



barbatulre, whicli would seem to be quite comparable to a 

 '' gregarinoid " movement. Again, Gray and Tullocli (24a), 

 in their description of T. gambiense in the fly (Glossina 

 palpalis), say that the parasites also progress in a zig-zag 

 manner, advancing by a series of contractions, which bend 

 first one side of the body and then the other (cf. the flexion 

 movements of sporozoites). In all such cases described, not 

 the flagellate end, but the non-flagellate end, goes first.^ 



(b) Agglomeration. 



Before considering the process itself, a few words are necessary witli 

 regard to its occurrence and causation. This characteristic phenomenon of 

 Trj'panosomes appears to take place chiefly or only upon the advent of 

 unfavourable biological conditions in the surrounding medium. As said 

 above, increasing scarcity of nutriment brings about its occurrence in the 

 case of Trypauomorpha, when in the Insectan host. In the normal, 

 unaltered blood, or other humour, of Vertebrate hosts, agglomeration has 

 onh' seldom been observed. A tendency to it has been noticed in T. 

 lewisi, and Prowazek has found it to occur in T. brucii, in the inner 

 organs of guinea-pigs and rats. In these cases the phenomenon does not 

 appear to be very persistent. Schaudinn also describes its occurrence in 

 T. ziemanni in the owl. This variety is often termed self- or auto- 

 agglomeration. 



On the other hand, when blood containing some of the parasites is 

 drawn off, defibrinated, and kept for some time at a low temperature^ 

 (in the refrigerator), agglomeration usually sets in partially, and con- 

 tinues more or less persistently, until the death of the parasites super- 

 venes. It is readily and, one may perhaps say, typically produced, when 

 the serum of an animal which has been two or three times inoculated with 

 its specific Trypanosome (e. g. T. lewisi, in the case of the rat), and which 

 is thus becoming repellent to, or acquiring immunity ^ against, that par- 



' For the importance of this fact see below, in Section XI. 



" It may be here mentioned that Trypanosomes appear to be much more 

 resistant to a lowering than to an increase of temperature. Their vitality, 

 in cold solutions, has a significant bearing upon the question of a cold- 

 blooded, alternate host. 



^ Without entering here into the question of how imniuuity is acquired, 

 it may be mentioned that this does not seem to stand in any relation with 

 the property of agglomeration. For one thing, the action of heat upon any 

 serum differs considerably as regards the destruction of its agglomerative 



