44 



METHODS OF CULTIVATION OF BACTERIA. 



FlG. 10. Blood serum inspissator. 



by which process a clear solid medium is obtained. " Inspissa- 

 tion " is probably an initial stage of coagulation, and is effected 

 by keeping the serum at 65 C. till it stiffens. This temperature 

 is just below the coagulation point of the serum. The more 

 slowly the operation is performed the clearer will be the serum. 

 The apparatus used is seen in Fig. 10. It consists of a rectan- 

 gular, shallow, covered, hot-water 

 jacket, with sloped bottom, and can 

 be rapidly heated by an S-shaped 

 Bunsen containing many lateral 

 perforations, from each of which 

 a flame issues. The serum tubes 

 are thus placed in a sloped posi- 

 tion, and the temperature being 

 raised to 65 C., the contents 

 solidify in a sloped position in the 

 interior. It is well not only to 

 have the jacket filled with water, 

 but also to put some water in the 



trough in which the tubes lie, and also to have a thermometer in the 

 water. This prevents cooling of the tubes when the lid is raised 

 to see if the process is complete. As is evident, the prepara- 

 tion of this medium is tedious, but its use is necessary for the 

 observation of particular characteristics in several pathogenic 

 bacteria, notably the tubercle bacillus. Pleuritic and other 

 effusions may be prepared in the same way, and used as media, 

 but care must be taken in their use, as we have no right to say 

 that pathological effusions have the same chemical composition 

 as normal serum. 



If blood be collected with strict aseptic precautions, then 

 sterilisation of the serum is unnecessary. To this end the mouth 

 of the cylinder used for collecting the blood, instead of being 

 plugged with wool, has an india-rubber bung inserted in it 

 through which two bent glass tubes pass. The outer end of one 

 of these is of convenient length, and, before sterilisation, a large 

 cap of cotton wool is tied over it; the other tube is plugged 

 with a piece of cotton wool. In the slaughter-house the cap is 

 removed and the tube is inserted into the blood-vessel as a 

 canula. The cylinder is thus easily filled. Another method is 

 to conduct the blood to the cylinder by means of a sterilised 



