254: Profei^finr Sheridan Delqjine [Feb. 13, 



at 5.20 p.m., on September 22. These pies were removed respectively 

 at 6.17 p.m. and 6.11 p.m. before Dr. Howarth and myself, and wo 

 immediately took the temperature of the central parts of the pies, and 

 also of the meat close to the bottom and top crust. 



I could not devise any more reliable way of doing this than by 

 plunging the bulb of the thermometer rapidly into the pie through 

 the vent hole. A continuous record of the changes of temperature 

 taking place in the pies during baking could not have been obtained 

 on the premises, and v^^ould not have offered great guarantees of 

 accuracy. The distance between the centre of the pie and the top 

 crust having been measured on the stem of the thermometer, the 

 instrument was plunged into the meat so that its bulb should reach 

 at once the centre of the pie. This undoubtedly allowed a little of 

 the boiling fluid which was on the surface of the meat to follow the 

 bulb, so that the temperature observed/ must have, in every case, been 

 higher than the actual temperature of the centre of the pie ; but the 

 error so produced was in the right direction, for it did not tend 

 to make one under-estimate the temperature. After allowing the 

 mercurial column to rise to the utmost, and seeing that it remained 

 stationary, the temperature was read, the bulb of the thermometer was 

 then pushed as far as the bottom crust, the temperature being again 

 taken, the bulb was now withdrawn so as to come almost in contact 

 with the top crust. As each of the ovens is heated chiefly by means 

 of radiators situated above the pies, it was to be expected that the 

 top crust would be hotter than the bottom crust. 



In a first set of observations I found that the highest temperature 

 reached in the central part of the pies was 47*2° C. These pies 

 were said to have been under-baked (fifty-one minutes instead of the 

 usual ninety minutes), but they had the appearance of well-baked 

 pies. 



In a second set of observations I found that the highest temperature 

 in the centre of the pies was 86*6^ C. These pies were said to be 

 over-bak(d (107 minutes instead of 90 minutes), and they looked 

 distinctly too much baked, their colour being much darker than is 

 usual. 



Several facts were brought out by these experiments. 



1. The temperature of the centre of a pie said to be under-baked, 

 hut having all the external appearances of being well-baked, may not 

 exceed 47*2° C A batcli oi pies prepared in a hurry mi^i therefore 

 be so cooked that bacteria might continue to grow in their centre during 

 the greater part of their stay in the oven, and the bacteria would 

 certainly not be killed * 



2. The temperature of the centre of a pie obviously over-baked, 

 and acknowledged to be so, had not gone beyond 86'6°C., which 



* The appearance of the portions of pies which I received from Dr. Howarth 

 at the begiiining of this enquiry, gave me the iniprestiou that these pies which 

 caused the Derby epidemic had been uuder-buked. 



