204 VETERINARY HYGIENE 



Steam under pressure is in constant use in laboratories for the dis- 

 infection of materials used in bacteriological work and for the 

 disinfection of instruments. 



Steam under Reduced Pressure. The temperature of steam 

 can be reduced by lowering the pressure under which it is generated. 

 The lower the temperature the less is the germicidal potency, so 

 that " reduced steam " by itself is of no value for practical dis- 

 infection. As ordinary steam may be deleterious to certain goods, 

 reduced steam may be used, and the deficiency brought about by 

 lowering temperature made up by combining with it such a sub- 

 stance as formaldehyde. 



There are various steam disinfectors on the market, some fixed, 

 such as are used by municipalities for the disinfection of clothing 

 from infectious houses, and others that are portable or built on 

 wheels for the convenience of transport, as may be required under 

 such conditions as warfare. The use of current steam gives the 

 best results, as the steam being drawn through the machine con- 

 taining the articles displaces and drives before it the air contained 

 in the folds and interstices of clothing, &c. This naturally facili- 

 tates the penetration of the steam. 



Saturated steam under a pressure of 10 Ibs. above normal atmos- 

 pheric pressure has a temperature of 240 F., and being under 

 increased pressure has great penetrating power, and good results are 

 obtained from its use. An exposure of twenty minutes is 

 sufficient to ensure the destruction of both bacteria and spores even 

 in folded blankets. After this exposure the steam is shut off and a 

 current of hot air is forced through; this thoroughly dries the 

 goods which come out none the worse for the treatment. Such 

 articles as leather are, however, spoiled. Cotton, woollen, and linen 

 fabrics stand the steam and heat well. Blood and similar stains 

 are unfortunately fixed. 



With Thresh's disinfector increased pressure is not used, but 

 the temperature of the steam is raised above that of ordinary 

 steam by using a saline fluid that boils at 225 F. ; current steam 

 is used. 



During the 1912 outbreak of foot-and-mouth disease in Ireland 

 all the stacks of hay on farms near the scenes of outbreaks were 

 disinfected by the agency of superheated steam. Steam was 

 injected from an engine into the ricks to a depth of 1-| to 2 feet. 

 The heat penetrated to a depth of over 3 feet. Repeated tests 

 with a thermometer showed a temperature of 220 F. 



It was found that this process did not damage the hay in any 

 way. The day after the steaming the hay was found to be quite 



