278 THE GROUSE IN HEALTH AND IN DISEASE 



have to be used in order to obtain colonies on solid culture media. It was 

 further recognised that the tissue would have to be crushed into a 

 making 30 pulp, which could be spread more or less evenly over the surface 

 fromthe f *h e medium, in order that any micro-organisms which might 

 C be present should have a chance of coming into contact with it. 



Moreover, it was clearly seen that in carrying out experiments of this 

 kind the chances of accidental contamination were not inconsiderable. The 

 methods which were first employed in Scotland were later somewhat modified 

 when the investigations were subsequently continued in Cambridge. 



The precise conditions under which these experiments were conducted are 

 matters of considerable importance, since upon them depend the reliability 

 of the results which were obtained. We have therefore no hesitation in 

 describing the methods in detail. 



Previous to beginning an experiment the room was carefully prepared. 



All dust was removed from the window ledges and elsewhere, and the floor 



and bench were flooded with a mixture of glycerine and lysol to 



Preoau- 6 J 



tions lay the dust. All the windows and ventilation shafts were closed 



against 



aerial con- during the actual operation of making the cultures. As a further 



tamination. . . ..,. i i i 



precaution against aerial contamination the tissues were crushed inside 

 a glass frame which was constructed as follows (PI. xxxix., Fig. 1) : Two 

 sheets of plate glass, 21x8 inches, formed the top and bottom respectively, 

 the former being supported on blocks of wood, which formed the sides. The 

 back also was formed of a sheet of plate glass, and the front was closed by 

 a curtain of linen, soaked in lysol, which could be partially turned back when 

 required. The joints of the frame were made draught-proof by means of 

 rubber tubing. On the floor of the frame another sheet of plate glass, which 

 extended the whole length, but was 3 inches narrower than the bottom, 

 was placed towards the back, so as to form a ledge near the centre of the 

 floor, upon which the plates used for crushing the tissues could be con- 

 veniently manipulated, and yet be covered by the roof. The height of the 

 frame from the top to this ledge was 3^ inches. 



Before use the frame was washed out with a mixture of glycerine and 

 lysol. In order to estimate the risk of aerial contamination agar plates were 

 exposed on the bench and inside the frame during the whole period of time 

 the cultures were being made. 



The birds, if living, were killed by decapitation, weighed and immediately 



