MICROSCOPICAL AND PHYSIOLOGICAL EXAMINATION. 11 



Schroder and Dusch (1854), who caused the air to pass 

 through cotton-wool filters, and by this means still obtained 

 the same result. 



The principles of the whole technology of sterilisation 

 being thus established, the matter under consideration reached 

 a high state of development and great importance both for 

 science and for industry, more particularly through Pasteur 

 and, subsequently, several other eminent scientists, who 

 devoted their energies to these investigations. 



1. Sterilisation of glass and metal articles. Sterilisa- 

 tion properly so-called must always be preceded by a thorough 

 mechanical and, in many cases, also a chemical cleansing. 

 Articles of daily use in the laboratory, as, for instance, spatulas, 

 pins, wire, etc., are heated directly in a flame and allowed 

 to cool in a germ-free space. Many pieces of apparatus, 

 however, do not admit of this treatment, and must be sterilised 

 either by heating in steam or in a water-bath, or else in dry 

 air by means of a sterilising oven, in which the objects are 

 heated for one or two hours at a temperature of about 150 C. 

 According to the nature of the objects, some may be put 

 directly into the sterilising oven, whilst others must be pre- 

 viously wrapped in paper. The necks of the flasks are closed 

 by cotton-wool, which is, in addition, often covered by several 

 layers of filter-paper. 



2. Sterilisation of nutritive liquids and solid nutritive 

 substrata. Nutritive liquids can be sterilised by filtration 

 or by heat. The former method presents the advantage that 

 the liquids treated undergo less change than when heat is 

 employed, and are, consequently, better suited for the develop- 

 ment of many species of micro-organisms. The necessary 

 condition for sterilisation is, that the pores of the filter must 

 be smaller than even the smallest micro-organisms. Gypsum, 

 asbestos, charcoal, and porcelain have been employed for this 

 purpose, the liquids being forced by pressure and suction 

 through thick layers of these substances. The form most 

 generally used is the Chamberland porcelain filter, which, 



