Gr. H. F. Nuttall 
285 
by means of this vector the trypanosomes have been successfully 
conveyed to Rana esculenta in which the flagellate does not occur in 
nature. 
Finally, T would mention T. vittatae which is parasitic in a tortoise 
{Emyda vittatae) in Ceylon. This flagellate is transmitted by a leech 
(Glossosiphonia) in which it appears to behave in a similar manner to 
the fish trypanosomes above enumerated. 
The general trend of recent work has gone to prove that, in the 
majority of instances, the trypanosomes of vertebrates are transmitted 
by blood-sucking ectoparasites within which they undergo a cyclical 
development. Whereas in the case of the Glossina mechanical trans¬ 
mission may occur it must play a subsidiary part. In Glossina, 
Gonorhinus and leeches infection occurs through the mouthparts of the 
vector; in most Glossinas the flagellates are expelled from the salivary 
glands. In but a single instance {T. inopinatum) has it been claimed 
that the offspring of the vector (a leech) becomes hereditarily infected, 
and the statement awaits confirmation. In the rat-trypanosome there 
occurs a contaminative infection through the dejecta of the fleas or lice 
which attack a fresh host. Fleas and lice do not become hereditarily 
infected with T. letuisi. In dourine {T. equiperdum) direct infection 
from host to host in the act of coitus appears to be the rule, whereas 
it may occur exceptionally in other trypanosome infections. We are 
still ignorant as to the usual mode of infection of many trypanosomiases, 
including Surra and Mai de Caderas. In both cases the parasites 
{T. evansi and T. equinum) possess a wide range of pathogenicity and 
may produce chrotric cases, so that there is every reason to believe, in 
my opinion, that reservoirs may play an important part in maintaining 
these diseases in nature. 
Powers of adaptation shown hy trypanosomes. 
Investigations conducted during the last few years have shown that 
trypanosomes possess considerable power of adaptation to altered 
conditions in the host, such as may be brought about by the ad¬ 
ministration of drugs. Trypanosomes may acquire a great resistance to 
the effect of a drug. At times this acquired resistance is accompanied 
by changes in their morphology, at other times no such changes occur. 
In the case of T. brucei, which becomes resistant to pyronin and oxazine 
preparations, the acquired drug-resistance is accompanied by the 
disappearance of the blepharoplast. If these drugs are administered 
