Pender-Herrick Thermistor

WLMD ID: akwa

Surgery, and anesthetics themselves, can change the body temperature of patients undergoing general anesthesia. During WWII, the anesthesiologist Dr. John William Pender (1912-2001) began seeking a better method of monitoring the temperature of his patients during surgery. In the decade following the war, he worked at the Mayo Clinic in Rochester, MN. There he met the biophysicist Dr. Julia F. Herrick (1893-1979), who had wartime experience in using temperature-sensing thermistors. At his request, Dr. Herrick built the thermistor shown here for Dr. Pender around 1946. At that time, the only other apparatus available (beside the traditional glass thermometer) was one that had been built for use in refrigerators. In his description of this thermistor, Dr. Pender noted that it was later replaced by a new, commercial device, the Tele-Thermometer.

Dr. Pender continued to advocate improvements in patient monitoring throughout his career. Dr. Pender pioneered anesthesia methods for cardiac surgery, and also invented a hands-free ether vaporizer. He was a founder of the Wood Library-Museum’s ongoing program to videotape interviews with leaders in the specialty. This is now known as the Pender Collection of the Living History of Anesthesiology.

Catalog Record: Pender-Herrick Thermistor

Access Key: akwa
Accession No.: 2011-02-04-2

Title: [Pender-Herrick thermistor-thermometer.]

Author: Herrick, Julia F. (Frances), 1893-1979.
Author: Pender, John William 1912-2001.

Title variation: Alt Title
Title: B-Y thermistor [before Yellow Springs].

Publisher: [Rochester, Minnesota] : [Julia F. Herrick], [between 1946 and 1954].

Physical Descript: 1 monitoring device : plastics, metals, wood, glass, paper ; 24.5 x 17 x 7.5 cm.

Subject: Monitoring, Physiologic – instrumentation.
Subject: Monitors.
Subject: Thermometers.
Subject: Temperature Measurement.

Note Type: General
Notes: The early year (1946) in the date range for the possible year of manufacture
is based on the year that Dr. Pender returned to the Mayo Clinic after
serving for four years during WWII. The late year (1954) in the date range
for the possible year of ‘manufacture’ is based on the year that Dr. Pender
left the Mayo Clinic in Rochester, Minnesota for Palo Alto California. In
paperwork that Dr. John William Pender donated with this device he estimated
that it was made by Dr. Herrick around 1946. He also stated that it, “was
used only a short time” as it was replaced by an early commercial thermometer
made by the Yellow Springs Co.

Note Type: General
Notes: The title is taken from the names of the two people involved in its creation
and from the name that Dr. Herrick gave it in the instructions she provided
to Dr. Pender; The alternative title, “B-Y thermistor,” (before Yellow
Springs) comes from paperwork that Dr. Pender donated with this device.

Note Type: Citation
Notes: Accession record 2011-02-04-2. Located at: the Wood Library-Museum of
Anesthesiology, Schaumburg, Illinois.

Note Type: Citation
Notes: Calmes SH. John William “Bill” Pender, M.D., 1912-2001. Bull Anesth Hist.
April, 2001;19(2):2-3.

Note Type: Citation
Notes: Herrick, Julia Frances (1893-?). In: Ogilvie M, Harvey J, ed. Biographical
Dictionary of Women in Science: Pioneering Lives from Ancient Times to the
Mid-20th Century. New York: Routledge; 2000:A-K 1190-1191. https://www.scribd.
com/doc/168217514/M-Ogilvie-the-Biographical-Dictionary-of-Women. Accessed
September 29, 2014.

Note Type: Physical Description
Notes: One thermistor based monitoring device; The sides and bottom are varnished
wood; The front is a black laminate; Nail heads are visible around the joints
of the device; Based on its construction, this seems to be a working
prototype rather than a manufactured or mass produced item; In the
upper-half of the front of the device is a round needle gauge covered with
glass; The face of the gauge is a donut cut piece of thick white paper; It is
marked in increments of .2, with the even, whole increments from 28 to 46
numbered; It is likely that these increments represent degrees Celsius; Below
the gauge are two round inputs; One is labeled, “BATTERY ADJUST”, and the
other is labeled “BALANCE ADJUST”; Below these is a turn switch with three
marked options for the pointer, “OFF”, “BATTERY”, “OPERATE”; To the left of
this switch are two small plugs; One is not marked and the other is labeled,
“THERMISTOR”; There are no other markings.

Note Type: Reproduction
Notes: Photographed by Mr. Steve Donisch, September 16, 2013.

Note Type: Acquisition
Notes: Donated to the WLM by John William Pender, M.D.

Note Type: Historical
Notes: This thermometer was made for anesthesiologist John William Pender, MD,
(1912-2001) by biophysicist Julia Frances Herrick, PhD, (1893-1979) after
they had both returned to the Mayo Clinic in 1946 following service during
World War II. This was before electronic thermometers to easily and
accurately measure rectal temperatures during anesthesia were commercially
available. Anesthesiologists monitor the body temperature of patients
undergoing general anesthesia, so that they may promptly detect and treat
deviations in temperature.

At Mayo, Dr. Pender was engaged in patient care and research in which
temperature monitoring was especially important and the only device available
to him was one made to measure temperatures in refrigerators. This was far
from ideal, but the use of electronic thermometers in medicine was in its
infancy. Dr. Herrick, assistant professor in experimental medicine,
constructed this thermometer for Dr. Pender using a “thermistor” or thermal

A thermistor is wire made of a temperature-sensitive material that ‘resists’
or decreases the flow of an electrical current in a way that is directly
related to the temperature of the wire. Using a thermistor, body temperature
could be accurately measured because the resistance could be measured, in
this case via a special circuit called a Wheatstone bridge.

The typewritten instructions that Dr. Herrick provided with the thermometer
reveal a tedious calibration process that called for two people, as well as
an interesting step before the reading of the temperature from gauge: “The
proper technique when reading most meters is to tap it gently … [otherwise]
there is a tendency for these pointers not to swing freely … .”

Dr. Pender reports that, before he left Minnesota for California in 1954,
this thermometer was replaced by a commercial electronic thermometer made by
Yellow Springs Instrument Company of Ohio.

Note Type: Publication
Notes: Alfonso S, Herrick JF. Experimental procedures for establishing reliability
of thermistors for measuring intravascular temperatures. Physiologist.
1960;3(4):63-69. https://dcprinciples.
org/publications/tphys/legacy/1960/issue4/63.pdf. https://dcprinciples.
org/publications/tphys/legacy/1960/issue4/index.htm. Accessed September 29,

Note Type: Publication
Notes: Herrick JF. History of bio-medical electronics art. Proc IRE. May,

Note Type: Publication
Notes: Herrick JF, Baldes EJ. The Termo-Stromurh method of measuring blood flow. J
Applied Physics. 1931;1(6):407-417.
Accessed September 29, 2014.

Note Type: Exhibition
Notes: Selected for the WLM website.