MICHIGAN ACADEMY OF SCIENCE. 
23 
tick, leech and the like which feed upon the infected animal may be- 
come a suitable soil for the disease organism in which case it multi- 
plies directly, or else it passes through a developmental cycle. It has 
been supposed by some that active carriers can harbor only animal 
parasites such as the pathogenic protozoa and certain worms (filoria) 
an assumption which is certainly erroneous. It is undoubtedly true that 
in the majority of known active carriers the organism which is trans- 
mitted is of an animal nature but that fact is not sufficient to exclude 
the bacteria, nor does it justify the assumption that an unseen and 
unrecognizable germ which is transmitted by an active carrier is ipso 
facto a protozoon. 
Too much stress can hardly be placed upon the fact that the ordinary 
bubonic plague, the cause of which is a typical bacillus, is spread al- 
most wholly by the bites of fleas which come from diseased rats, ground 
squirrels and other rodents. The isolation of the diseased patient is 
not enough to prevent new cases from developing. The protective meas- 
ures must include the utmost eradication of rodents and their ecto- 
parasites. 
The splendid studies of Rickett’s have shown that the so-called “Rocky 
Mountain Fever” or Spotted Fever is in all probability due to a bacillus, 
and furthermore that it is invariably transmitted by the bite of a tick 
or of its offspring. 
Other examples of active carriers of bacterial organisms are met with 
in connection with certain spirochete infections, of birds, mammals and 
man. The best example of the latter type of infection is the African Tick 
Fever. The active carrier in this case is a tick ( Ornithodorus moutata ) 
and the disease is transmitted not only by the tick but also by its offspring. 
In other words, we have here, as in the case of Texas fever, and Spotted 
Fever, a hereditary transmission of the parasite from the parent through 
the egg to the young tick. Instances of such hereditary transmission 
are common enough in the case of the Tick family but are rather ex- 
ceptional with the mosquito and other insects. 
Our knowledge regarding the changes which the spirochete under- 
goes in the tick and in the egg is by no means fully established. While 
some worker, such as Koch, have described the presence of the spiral 
organism in the internal organs and in the eggs, other observers have 
failed to demonstrate their presence. The recent observations of 
Leishman are pregnant with future possibilities and for that reason call 
for a brief mention. Leishman in his work was unable to detect recog- 
nizable spirochetes in ticks, later than the 10th day after ingestion. 
Instead he observed clumps of chromation granules which were also in- 
variably present in the eggs, larvce and nymphs derived from infected 
ticks. Whether these granules are of spirochete origin is uncertain, 
for Leishman himself found similar granules in nymphs derived from 
ticks fed on normal blood. Inoculation of suspensions of such granules, 
which apparently contained no spirochetes, gave the typical infection 
in mice. Future work must determine the real significance of the 
Leishman granules. If it should be proven that the granules represent 
a developmental phase of the spirochete it would in some measure up- 
hold the view of Much, Fontes and others that the tubercle bacillus is 
capable of existing in a similar form. 
It has been heretofore quite generally accepted that the transmission 
