4 o THOMPSON YATES LABORATORIES REPORT 
time for the culture tubes to become heated ; whereas, if water is in the inner chamber, 
and the culture tubes put in when the thermometer registers 8o° C, it is found that 
there is only a fall of 10 to I5°C, and the thermometer rises to 70 0 C, in a few 
minutes. 
The tubes are left in for 15 to 20 minutes after the thermometer has risen 
again to 70 0 C, so during that time they will have been kept at between 70 0 C. and 
8o° C, and for most of the time over 75 0 C. 
The apparatus should be made in beaten copper and spun afterwards ; any 
local coppersmith should be able to make one at the cost of about £1 5s. 
DESCRIPTION OF PHOTOGRAPHS OF CULTURES OF B. PESTIS 
IN BROTH SHOWING 'STALACTITE' FORMATION 
By Balfour Stewart, M.A., M.B. Camb. 
Plate IV. Figs. 7 and 8 
Fig. 7 is a photograph of a culture of B. pestis in a flask of broth ; several ' stalactites ' are 
seen growing near the side where they come into focus. 
Fig. 8. ' Stalactite ' growth of B. pestis in a flat flask (Soyka's flask). The light was 
behind, and was thrown in parallel rays by means of a lens. Between the lens and the flask was an 
alum bath to stop the heat rays from the incandescent lamp ; without this it was found that diffusion 
currents were set up, and the ' stalactites ' moved during the time of exposure. In front of the 
flask was a black screen to cut off the reflection from the edges of the flask, an opening was cut 
corresponding to the lower half of the flask, the upper edge of the cut out portion just allowed the 
surface of the broth to show. 
At the left are seen several long thread-like growths ( ' stalactite ' growth of Haffkinf.) 
hanging from small particles of butter floating on the surface. 
At the right is seen a denser growth, which does not show individual 'stalactites.' 
The flask was inoculated by means of a glass rod infected with plague culture. The rod 
was pushed down into the broth. The rod is seen to be covered with growth, which has crept 
up the rod and spread out over the surface of the broth, the substance of the broth remaining clear, 
except where some isolated colonies have grown on the sides of the flask. 
