645 
thus obtained is now treated with two drops of a 2 per cent solution of para- 
phenylenediamin and one drop of a solution of 2 per cent hydrogen peroxide. 
When thus treated not more than a perceptible blue color shall be obtained 
within thirty seconds after mixing. 
Rule 6. Pasteurizing temperatures . — All pasteurized milk, cream, skimmed 
milk, milk products, and milk and cream used in the production of milk prod- 
ucts shall be pasteurized in accordance with the following regulations : 
(A) Continuous pasteurization : In all continuous pasteurization the milk and 
cream shall be heated to a temperature which shall be determined and fixed by 
the department of health for each machine at a point corresponding to the 
temperature required to kill 99 per cent of the bacteria and all pathogenic 
bacteria contained in the raw product. For this determination ordinary raw 
milk containing in the neighborhood of 3,000,000 bacteria shall be used and the 
pasteurized product shall be collected as it fiows from the cooling apparatus. 
All continuous pasteurizers shall be equipped with a feeding pipe which 
is so constructed that the pasteurizer can not be fed in excess of its normal 
working capacity ; that is, in excess of the working capacity of the machine at 
which 99 per cent of the bacteria are killed when the required amount of heat 
is applied. 
All continuous pasteurizers operated outside of the city limits, for the produc- 
tion of pasteurized milk and milk products to be sold in the city of Chicago, 
shall be equipped with an apparatus regulating automatically the supply of 
steam and heat, so as to correspond with and produce the required temperature 
of the outflow of the pasteurized product. These automatic thermoregulators 
shall be accurate, and must be approved by the commissioner of health before 
being installed. 
A recording apparatus shall be installed upon all continuous pasteurizers 
operated within the city limits so as to record during operation the temperature 
of the pasteurized product as it flows from the heater. The thermometer of 
this recording apparatus must be accurate and kept emerged in the milk in such 
a way that it is not exposed to escaping steam or other heat, except the heated 
milk. 
The records made by this recording thermometer must be accurate and made 
in a chamber which is kept under lock and key in the control of the department 
of health. 
The automatic thermo regulating and recording apparatus may be combined 
into one instrument, and it is recommended that all i^asteurizers be equipped 
with both appliances or the combination apparatus. 
(B) Held pasteurization: Whenever milk is held during pasteurization in 
such a manner that the process of pasteurizing is not a continuous one, namely, 
a continuous flow of milk through the heating or heat-retaining chamber, the 
process shall be designated as “ Held pasteurization.” Such methods of pas- 
teurization and pasteurization appliances or systems installed and used shall 
be examined and approved by the commissioner of health, or his duly appointed 
representatives, when all of the following requirements are fulfilled: 
1. When the pasteurized product shows that over 99 per cent of the bacteria 
and all pathogenic bacteria contained in the raw product have been destroyed. 
2. When the mechanism of the pasteurizer or pasteurizing system is such that 
the three important elements, namely, the temperature, time of exposure, and the 
quantity of milk exposed at one time, can be readily kept under control and ob- 
servation by the department of health. 
3. When the following conditions are complied with : 
