PREPARATION OF DILUTIONS 

 The following table shows the details of various dilutions: 



In preparing these dilutions, it is best to measure off the small quantities o.i- 

 i c.cm. with a pipette; allow this to run into a well-graduated measuring glass and add 

 enough saline to make the required dilutions. For example, if 30 c.cm. of a dilution 

 i : 100 is desired, 0.3 c.cm. should be measured off with a pipette and aUowed to flow 

 into a 50 or 100 c.cm. graduated cylinder and saline solution added up to 30.0 c.cm. 



It should always be one's aim to get along with small quantities of the substance 

 to be diluted. If, for example, 8 to 10 c.cm. of a toxin dilution i : 100 are required o.i 

 c.cm. of toxin +9.9 c.cm. of saline should be taken and not i c.cm. of toxin and 99 c.cm. 

 of NaCl sol. 



Before making any dilution one should always calculate the total amount of sub- 

 stance required; as for example in the following experiment: 



1. Animal o.i c.cm. Toxin subcutaneously 



2. Animal 0.05 c.cm. Toxin subcutaneously 



3. Animal o.oi c.cm. Toxin subcutaneously 



4. Animal o.ooi c.cm. Toxin subcutaneously 



Here, the total quantity of toxin necessary is found, by adding, to be 0.161 c.cm. 

 This represents the minimum amount. It is always advisable to make an allowance 

 for some loss and at the same time bring up the amount to a round or even number. 

 0.2 c.cm. of toxin would fulfill all these requirements. This amount is measured off 

 by a pipette, placed into a graduated cylinder and saline added up to 2.0 c.cm., making 

 a dilution of i : 10. Then 0.2 c.cm. of this dilution (i : 10) is taken, placed into another 

 graduate, and again diluted with saline up to 2.0 c.cm. thus making a dilution of 

 1:100. The above problem therefore of injecting the various animals, ran be com- 

 pleted as follows: 



1. Animal receives i c.cm. of dilution i : 10 



2. Animal receives 0.5 c.cm. of dilution i : 10 



3. Animal receives i c.cm. of dilution i : 100 



4. Animal receives o.i c.cm. of dilution i : 100 



