8 LECTURES ON IMMUNITY 



veins of the animal ; as a special case may be regarded the 

 " intracardial injection" directly into the heart of the ani- 

 mal. More slowly acts the " intraperitoneal injection " into 

 the peritoneum, and still more so the "intramuscular injec- 

 tion," or the "subcutaneous injection," under the skin of 

 the animal. This last method is very much used. In 

 these cases the injected body reaches the blood very 

 slowly, in which fluid it produces antibodies. The anti- 

 bodies may be divided into two great groups according to 

 the nature of the injected fluid, whether it is a homogene- 

 ous solution or an emulsion of cells, e.g. bacteria or red 

 blood corpuscles. These suspensions of, e.g., erythrocytes 

 are secured by centrifugating blood freed of fibrin. Be- 

 tween the centrifugalized blood corpuscles there still 

 remains a noticeable quantity of normal serum. This 

 serum contains a very effective reagent for most of the re- 

 actions which we wish to study. It is therefore necessary 

 to wash it away. For this purpose we use a so-called 

 physiological solution, in most cases of sodium chloride 

 (0.8-0.9 %) Suspended in this solution blood corpuscles 

 and most bacilli remain unaltered. In stronger solutions 

 the corpuscles or bacilli contract; in weaker solutions 

 the erythrocytes give up their red colouring matter and 

 remain colourless (" stromata "). The bacilli are injured 

 by plasmolysis or imbibition of water. To be washed, the 

 blood corpuscles are shaken with the physiological solu- 

 tion, centrifugalized, separated, and this operation repeated 

 until the serum is washed away as much as necessary. 

 Usually two or three washings with five times the amount 

 of solution are sufficient. 

 The antibodies produced after the injection of a homo- 



