i8 



LABORATORY EQUIPMENT. 



The fluid to be filtered is placed into the glass cylinder and sucked through into the flask 

 by means of a vacuum which is here produced. For the purpose of collecting very small 

 quantities a test-tube may be placed into the exhaust flask (Fig. 12). 



Preparation of Dilutions and Measurement of Small Amounts of 



Bacteria. 



All serological methods are to be considered on quantitative bases. In 

 serum diagnosis as well as in the therapy, the amount of the serum employed 

 is the deciding factor. Similarly, the number or amount of bacteria required 

 either for the purposes of immunization or serological reactions is of extreme 

 importance. 



One cubic centimeter is the unit of measure for serum and all fluid material 

 (Bouillon cultures, exudates, etc.). // small quantities are required, it is 

 best to dilute the fluid with 0.85 per cent, saline solution. The exact preparation 

 of dilutions is one of the most essential technical procedures of all serum diagnosis. 

 Some general rules may be of help. 



Never should amounts less then o.i c.c. be measured out directly. For 

 beginners even o.i is best measured in the form of a dilution, as errors are 

 apt to occur very easily. 



2. The decimal system should be adhered to as much as possible. 



3. The dilution should be made just before it is to be used, inasmuch as 

 many substances retain their activity best, or only, in concentrated form. 



The following is an example of correct forms of dilution: 



The stock dilution of i : 10 is made by measuring off i c.c. of toxin an adding 9 c.c. 

 of 0.85 per cent, of saline. 



The dilution i : 100 can be made by taking i c.c. of toxin and adding 99 c.c. of saline. 

 It is more practicable, however, to take i c.c. of the i : 10 stock dilution and add 9 c.c. 

 of saline. If the dilution i : 10 is not present and only a small amount of the dilution 

 i : 100 is desired, the latter is made by taking o.i toxin : 10.0 NaCl sol. Similarly 

 i : 1000=0.1 : 100= i c.cm. of the dilution (i : 10) : 100= i c.c. of the dilution (i : 100) : 

 10.0. 



