228 STATE BOARD OP AGRICULTURE 



heat, chemicals and filtration, heat undoubtedly occupies the foremost 



place. 

 Heat. This agent has been used since the embryonic days of bac- 



teriology. It was then applied continuously for various lengths 

 of time; but as shall be seen later, the experiments were not always suc- 

 cessful. Thanks to Tyndall for the introduction of discontinuous heating, 

 or what is commonly called fractional sterilization. Under the consider- 

 ation of spores it will be remembered that the spore wall was exceedingly 

 resistant, much more so than the vegetative form ; that some spores will 

 withstand several hours of steam heating. Consequently it is sought to 

 kill the vegetative form, which is done in a comparatively short time, and 

 the spore is then allowed to develop. The process is this: When the bac- 

 teria in the vegetative form are killed the heat is discontinued and the 

 spores are allowed to germinate The bacteria resulting from this germi- 

 nation are then subjected to another heating of the same time and degree. 

 This alternation of heating for the killing of bacteria, and cooling for the 

 germination of spores is repeated two or three, times, during which period 

 all the spores germinate and the bacteria produced from them are extermi- 

 nated. Two methods have been suggested of applying heat, continuous 

 and discontinuous, of which the discontinuous is the most reliable. 

 Wherever heat of a high degree is possible, continuous heating becomes 



feasible and even desirable in many instances. 

 Kinds. For sterilizing purposes, heat appears in two forms, moist 



and dry. 

 ^Boiling and steaming, without pressure, at 100° C. [212° F.], or with 

 pressure at 125° C. [257 F. ], illustrate the different manner of usage. 



Since boiling may be executed under most circumstances, and 

 SoiUng. the apparatus for steaming is not common, the former, boiling, 



is the most worthy of consideration. The conditions are almost 

 universally present to sterilize by boiling in the form of wash-boiler, 

 kettle, pans, or almost any receptacle. If utensils can be boiled for one- 

 half hour they are practically sterile; that is, they are about as sterile as 

 it is possible to obtain open vessels which are to be used in the handling 

 of exposed material. Occasionally spores are present which will resist this 

 process, yet this is not the usual case. If bottles or pails are to be pre- 

 pared for Pasteurized milk, no better means free from expense and trouble 

 could be adopted. From the hygienic side, boiling is again exceedingly 

 useful. Milk may be Pasteurized by boiling, and made free from infec- 

 tious bacteria. To insure safety against the tubercle bacillus, diphtheria 

 bacillus, or the typhoid bacillus, no better scheme could be devised than 

 to bring the milk to the boiling point for a moment at least. Water, too, 

 is often the host of the typhoid bacillus, cholera spirillum and occa- 

 sionally of other infectious bacteria. To rid it of danger, boiling is all that 

 is necessary. Contagious diseases often exist in families. The rooms 

 where the patients live have curtains and carpets, the beds have linen 

 and other coverings, the patients have clothing, — all of which may usually 

 be disinfected or absolutely cleansed by boiling. The scope of boiling as 

 a sterilizing, Pasteurizing or disinfecting agent is therefore very wide. 



