36 
PATHOLOGY: J. B. MURPHY 
Proc. N. a. S. 
is characterized by a lymphoid infiltration of the tissues around, and later, 
an actual invasion of the graft. 
We first showed that there was an actual increase in the circulating 
lymphocytes, accompanied by hyperplasia of the lymphoid elements 
following cancer inoculation into immune animals. If this crisis was pre- 
vented by the destruction of the lymphoc)rtes the immunity of the animal 
was destroyed. Furthermore, animals with tested immunity could be 
rendered susceptible by a similar destruction of the lymphocytes. The 
method we used for the destruction of the lymphocytes was that of small 
repeated doses of X-rays. It was established that this procedure would 
practically deplete the animal of lymphoid tissue without apparent injury 
to other important structures and without detectable influence on the 
animal's general health. 
In the course of this investigation of the action of X-rays it was noted 
that while repeated small or a single large dose would destroy the lymphoid 
tissue, a single, small exposure to a ray of suitable quality would stimulate 
the lymphocytes. The stimulation was judged by the numbers of circu- 
lating lymphocytes and the state of activity of the germinal centers in 
the spleen and lymph nodes as indicated by the number of mitotic figures 
present. This method of increasing the lymphoid elements of the body 
was first used in an attempt to increase the resistance of mice to replants 
of their own spontaneous tumors. By this treatment we increased the 
resistance from 3.4% in our control series to 50% in the treated series. 
By a similar induced lymphocytosis we have been able to develop a re- 
sistance to transplanted cancers which compares most favorably with the 
immunity following tissue injection. The procedure here was to expose 
a number of mice to a stimulating dose of X-rays and then inoculate them 
with a transplantable cancer a week later, at the same time inoculating 
a series of controls. The following table gives the result of these experi- 
ments : 
EXPERIMENT NUMBER I II III AVERAGE 
Takes in X-rayed mice 25.0% 29.0% 28.6% 27.5% 
Takes in control mice 77.8% 87.5% 60.0% 75.1% 
We next turned our attention to finding other methods of producing 
lymphoid stimulation. Several agents have been found other than X- 
rays, but only one so far which gives a reaction extensive enough and of 
sufficient duration for experimental purposes. Dry heat ranging from 
55 to 65° C. applied to the whole animal for five minutes was found to 
produce a stimulation of the lymphocytes and of lymphoid tissue of 
marked intensity, the increase in the number of lymphocytes persisting 
for a number of days. Mice treated in this manner and then inoculated 
with cancer a week later showed a striking degree of immunity as com- 
pared with the control animals inoculated with the same tumor at the 
same time. The following table gives the result of these experiments: 
