ATTENUATION OF VIRUS. 201 



by means of a drop of glycerine attached to a 

 glass slide, Pasteur has proposed to collect them 

 by passing a current of air through a glass tube 

 containing a loosely-packed filter of gun-cotton. 

 This is subsequently dissolved in ether, and, upon 

 evaporation of the ether, the particulate atmos- 

 pheric impurities are found in the film of collodion 

 remaining. 



Examination of Water. The bacterial flora of 

 water from any source may be studied by the 

 method already referred to in speaking of rain- 

 water ; viz., by using a small quantity to inoculate 

 a variety of sterilized organic infusions, and ob- 

 serving the development of the various micro- 

 organisms which make their appearance as the 

 result of this procedure. 



Dr. Angus Smith of Manchester has recently 

 given a favorable account of results obtained by 

 the gelatine method proposed by Koch. Pure fish- 

 gelatine is added to the water to be tested, in 

 sufficient quantity to form a gelatinous mass. If 

 the water is pure, this remains for a long time un- 

 altered ; but, if impure from the presence of living 

 organisms, the gelatine becomes liquefied in the 

 vicinity of these, and little bubbles are formed, at 

 the bottom of which the bacteria will be found. 



6. ATTENUATION OF VIRUS. Various methods 

 of producing physiological varieties of pathogenic 

 bacteria, to be used in protective inoculations, have 



