i6 



LABORATORY EQUIPMENT. 



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 placed into a brown glass tube and 

 sealed. 



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

 drops of isotonic salt solution at a temperature of 30 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 fromLautenschlager, 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 the harmful effects of light, room, body temperature, and chemical 

 substances like phenol is increased, but the thermolability of the complement remains the 

 same. Drying of 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 bacteria 

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

 centrifugalization or filtration. The first method does not completely free 



FIG. 9. 



Pukal-filter. 



FIG. 10. Filtration through a 

 Pukal-filter. 



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

 tial. In this connection, however, one must bear in mind, that many albu- 

 menous, 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 



