31 
In order to determine the length of time required for the various 
stages of development of the parasite, as well as to study them in 
detail, a number of mites were artificially infected, or, more properly, 
the usual manner of infection Avas controlled. For this purpose it 
was necessary to haA^e a supply of normal mites. Fortunately these 
chuld be readily obtained. The stable in AAdiich the infected rats had 
been kept contained a large room in AAdiich AA^ere a number of rat 
cages. In Iaa'o corners large single isolated cages had been built. 
One of these contained infected rats ; the other had been emptied of 
rats about tAA^o AA'eeks. Upon examination both AA^ere found to contain 
damp straAv and grain, upon AAdiich AA^ere myriads of mites. In the 
empty cage the mites AA^ere found to be free of infection. Six healthy 
rats, fresh from the dealer, AA’ere placed in this cage. In a very short 
time each rat AA^as infested AAdth a large number of mites. 
To remove the mites, AAdiich run about AAdth considerable rapidity 
upon the hair and skin, the rats are seized by the loose skin at the 
nape of the neck AAdth the tip of a pair of long clamps. The tail of 
the animal is grasped AAdth one hand and by traction the body is 
extended along the blades of the forceps. In this position it is easy 
to remoA^e the mites AAdth a fine-toothed comb, from AAdiich they are 
quickly shaken by a tap of the finger into a large glass jar. The 
inside of the rim of the jar should be preAdously smeared AAdth a ring 
of A'aseline, AAdiich the mites AAdll not traverse. In this manner it is 
possible in a short time to collect seA^eral hundred. 
The mites are kept in the jar seA^eral da^^s to starA^e them and then 
placed upon infected rats. For this purpose four rats AA’ere selected 
in AAUose blood the parasites AA^ere A^ery numerous. To transfer the 
mites to a rat it is only necessary to place the latter in the jar for a 
feAV minutes. In a short time all the mites Avill liaAX crawled upon 
the rat and concealed themselves in the fur. 
After six, tAA’eUe, eighteen, tAA'enty-four, tliirty-six, and forty- 
eight hours, mites AA^ere remoA^ed and examined in fresh preparations 
and stained smears, and a number presexA^ed in fixing solutions. 
From these paraffin serial sections Avere made. After forty-eight 
hours a large number of mites AA^ere removed and placed upon 
health}^ rats in order that the parasites then present in the mites 
might deA^elop AAdthout admixtures of younger stages, AA'hich Avould 
have been the result of continued feeding upon the diseased rats. 
At intervals of tAA^enty-four hours a number of these mites AA'ere 
removed and examined and sections made. Successive collections 
of mites Avere fed upon infected rats in order to obtain a large num- 
ber of infected mites for later experiments. 
In order to study the effect of the digestive juices of the mite upon 
encysted parasites in the rat’s blood, the folloAAung experiment Avas 
performed a number of times. The various stages of the process 
