STERILIZATION. 55 



serve when there is danger of the sterilizer boiling dry. Over 

 the top there is a tight-fitting cover. The steam is generated 

 by a Bunsen burner standing underneath. A perforated shelf 

 placed some distance above the surface of the water is for the 

 reception of the tubes and flasks that are to be sterilized. 



The sterilization of Hood-serum sometimes has to be performed in a specially 

 devised sterilizer, when a clear, fluid medium is desired. In this case the 

 serum is heated for an hour on each of six consecutive days to a temperature 

 of only 58° C. To obtain a transparent but solid medium the serum is kept 

 at a temperature of 75° C. for an hour on each of four consecutive days. The 

 process must be conducted carefully to avoid clouding of the serum. 



Pasteurization. — The name pasteurization has been ap- 

 phed to the partial steriHzation of substances at a compara- 

 tively low temperature. It is employed particularly for milk. 

 The temperature used (70° to 75° C. for 20 to 30 minutes) is 

 sufi&cient to destroy all ordinary pathogenic bacteria; for 

 example, the bacilli of tuberculosis and typhoid fever. Further- 

 more, the great majority of the saprophytic bacteria are de- 

 stroyed, and milk which has been pasteurized will remain un- 

 changed for several days, if kept cool. Its application is 

 principally in the feeding of infants when ordinary milk has 

 been found to produce undesirable results. Freeman* has 

 invented a pail of special form for the pasteurization of milk in 

 bottles. This pail is filled with hot water and the bottles are 

 placed in it; it has been foimd to keep up a temperature of about 

 75° C. 



The Autoclave, — The autoclave is an apparatus designed for 

 sterilization by steam under pressure. It was invented in France, 

 but is now used extensively in all parts of the world. Steam 

 generated at the ordinary atmospheric pressure is much less 

 destructive to bacteria, and especially to their spores, than 

 steam in the autoclave at a pressure of an additional one-half 

 to one atmosphere; the steam then reaches a temperature of 



* Medical Record. July 2, 1892, and August 4, 1894. This pail is sold 

 by James T. Dougherty, 411 West Fifty-ninth Street, New York. 



