i6 



LABORATORY EQUIPMENT 



forms a yellowish-red horny mass which is scraped off from the dish and ground up in 

 a mortar into a yellowish powder. The serum powder is then sealed in a brown 

 glass tube. 



When this dried serum is to be used, the tip of the ampoule is broken off, and several 

 drops of isotonic salt solution at a temperature of 30 C. are poured in, in just sufficient 

 an amount to moisten the wall of the glass tube. By rolling the tube to and fro, one 

 finds that the serum powder will easily stick to the moistened wall. The granules are 

 allowed to swell up and after they have done so, enough isotonic salt solution is added 

 to make up the original volume. 



For the preservation of thermolabile substances, the method of freezing has been 

 suggested. Morgenroth has devised for this purpose a simple and handy apparatus 

 named Frigo which can be obtained from Lautenschlager , Berlin. Although for most 

 tests this method of preservation has been employed with success, Neisser's clinic 

 reports that sera preserved in the Frigo with the idea of retaining their complement 

 did not give as accurate complement fixation experiments as did similar fresh sera. 



Friedberger advises the addition of 8 per cent, salt solution for the preservation of 

 the complement. When the serum is to be used it is diluted tenfold with distilled 

 water, so that a 10 per cent, dilution of complement is obtained. By the addition of 

 the salt, the resistance against harmful effects of light, room and body temperature, 

 and chemical substances like phenol is increased, but the thermolability of the com- 

 plement remains the same. Drying a serum in a desiccator is not to be advocated 

 for the preservation of the complement, as during such procedure a portion of the 

 complement is lost. Once the serum is in its dried form, however, the remaining 

 complement is retained and in addition, has become resistant against high heat. 



Filtration of Bacteria. 



It is important in many serological studies to be able to separate bac- 

 teria from their fluid media or suspension. This is accomplished either by 

 centrifugalization or filtration. The first method does not completely 



FIG. 9. Pukal filter. 



FIG. 10. Filtration through a Pukal filter. 



free the fluid of its bacteria, but if this is desired the method of filtration is 

 essential. In this connection, however, one must bear in mind that many 

 albuminous, or albumen-like substances, few colloids and even some toxins, 

 do not pass the filters and are therefore held back. Bacterial filtration is 

 simplified by preliminary centrifugalization or passing the fluid through 



