132 LABORATORY BACTERIOLOGY 
3 hours suffice for'the coagulation. When serum containing 
chloroform is to be coagulated, I am in the habit of placing 
the tubes for an hour or longer in a water bath at 55° to 60°C., 
or under the receiver of an air pump, to drive off the antiseptic. 
This procedure dispenses with all sterilization excepting that 
going on during the coagulation of the serum. It prevents the 
gradual formation of membranes of salts, which, remaining on 
the surface during coagulation, form a film unsuited for bacteria. 
Tubes of coagulated serum should be kept in a cold, closed 
space where the opportunities for evaporation are slight. They 
should always be kept inclined. 
‘The ordinary cotton-plugged test tubes I do not use, because 
of the rapid drying out permitted by them, as well as the 
opportunities for infection with fungi. Instead, a tube is used 
which has a ground glass cap fitted over it. This cap contracts 
into a narrow tube plugged with glass wool. This plug is not 
disturbed. The tube is cleaned, filled, and inoculated by re- 
moving the cap. With sufficient opportunity for the inter- 
change of air little evaporation takes place, and contamination 
of the culture is of very rare occurrence. In inoculating these 
tubes, bits of tissue, which include tuberculous foci, especially 
the most recent, are torn from the organs and transferred to 
the serum. Very little crushing, if any, is desirable or neces- 
sary. I think many failures are due to the often futile attempts 
to break up firm tubercules. Nor should the bits of tissue be 
rubbed into the surface, as is sometimes recommended. After 
a stay of several weeks in the thermostat, I usually remove the 
tubes and stir about the bits of tissue. This frequently is the 
occasion fora prompt appearance of growth within a week, as 
it seems to put certain still microscopic colonies in or around 
the tissue into better condition for further development. The 
thermostat should be fairly constant, as urged by Koch in his 
classic monograph, but I look upon moisture as more impor- 
tant. If possible, a thermostat should be used which is opened 
only occasionally. Into this a large dish of water is placed, which 
