228 



H. M. WOODCOCK. 



although tliey may have been, in certain eases, kept for a long while in 

 artificial surroundings. Indeed, their vitality and ability to recuperate 

 themselves and give rise to a fresh succession of parasites,^ if involution 

 has not proceeded too far, is sometimes nothing less than remarkable. For 

 instances and experiments showing this, reference should be made to the 

 works of Laveran and Mesnil, Lignieres, Sivori and Lecler, and others. 



The course which involution takes varies somewhat in different cases, and 

 the process may be considered as following one or another of three lines, 



R — -^- p 



Fig. 21. — Involution and degeneration forms of different 

 Trypanosomes. For description see text. A — E, T. gambiense 

 (a, C, and E after Bruce and Nabarro; B and d after Castellani). 

 F, K — P, T. brucii (f after Bradf. and Plim.; K — P after L. and 

 M.) G — J, QandE, T. equinuni (after Lignieres). s,T. brucii, 

 plasmodial mass, from spleen-pulp (after Bradf. and Plim.). 



which, though here dealt with separately for convenience, are, of course, 

 occasionally to be met with in combination in any given abnormal form. 

 These three directions are — (a) Cbromatolysis, (b) vacuolisation, and 

 (c) change of form. 



(a). In cbromatolysis, either there is a more or less complete loss by the 

 nucleus (i. e. the trophonucleus) of its chromatic constituents, which in 



* Hence their virulence and power of infection. 



