164 
E. A. MINCHIN AND H. M. WOODCOCK. 
that the cell has been disorganised artificially in making the 
film. Most of the free forms are more or less uniformly 
dispersed, however, and have no broken-down remains of a 
red cell in their vicinity. This fact, and, of course, the 
occurrence of these forms in the fresh preparations, makes it 
certain that their liberation is not due merely to manipulation 
of the blood. These free forms are undoubtedly present in 
the blood in the bird, scanty or numerous as the case may 
be. We are left somewhat uncertain, however, whether the 
process of liberation is an active or passive one on the part of 
the parasites, i e. whether the Halteridia leave the red 
blood-cells of their own accord, by breaking out or away 
from them, or whether they are simply set free by the 
rupture of a used-up corpuscle, which has probably contained 
several parasites. Scliaudinn maintained, of course, that the 
intra-cellular Halteridia regularly become active and trypani- 
form, and voluntarily leave the corpuscles. We should have 
seen this process in owls 19 and 23 if it occurs. On the 
whole, we are much more inclined to think the hitter explana- 
tion we have suggested is the true one. In this connection it 
is important and interesting to note that there is markedly 
little or no hypertrophy and enlargement of the red blood- 
corpuscles by the Halteridia, even when there are several 
individuals in one host-cell; this contrasts strikingly with the 
great enlargement and stretching which the red cells may 
undergo when infected with Haemogregarines or Haemo- 
cystidiura, for example. Hence it seems to us most likely 
that in an abundant infection, when there are three or more 
Halteridia in a corpuscle, their growth and increase in size 
renders it only a question of time before the corpuscle is 
ruptured, thus passively liberating the enclosed parasites. 
We should say it is very doubtful whether such free forms 
become again intra-cellular. 
Mayer, in his account of the parasites of another owl, 
Sy rn iu m al uco, also admits that he sought in vain for active 
trypaniform phases (trypanosome-forms) of the Halteridium. 
Before leaving this question we should like to put forward 
