SECTION III. 



OBSERVATIONS UPON THE PRECIPITIN AND PRECIPITABLE 

 SUBSTANCE IN CORPORE. 



We have seen that precipitins appear in the serum of suitable 

 animals after a longer or shorter treatment with non-homologous 

 albuminous substances, serum, milk, bacterial filtrates etc., administered 

 by intraperitoneal, subcutaneous, or intravenous injections or by excessive 

 feeding. The increase in the amount of precipitin is gradual, as is the 

 case with other immune substances, a fact that can be readily deter- 

 mined by occasionally bleeding the animal and testing its serum upon 

 the blood with which it has been treated. Obermayer and Pick (1902) 

 noted occasional differences in this respect in animals treated with 

 different blood components, some of which produced no effect at first 

 but great effects in the later stages of treatment, whereas in other 

 cases the increase was gradual. In accordance with what has been 

 observed with regard to the antitoxin of diphtheria in the horse and 

 the goat, by Salomonsen and Madsen (iv. 1897) (see p. 9) and others, 

 the amount of precipitin present in the serum of the animal during 

 immunization falls after each injection of the precipitin-producing 

 substance, the fall being succeeded in due course by a rise. Curves 

 made by roughly estimating at frequent intervals the amount of 

 precipitin present show that during successful treatment precipitin is 

 gradually formed within the animal's body. No measurements of the 

 amount of precipitin during the growth of immunization have as yet 

 been made, which would correspond to those made upon antitoxin, but 

 it is safe to say that a corresponding undulation would be observed. 

 Numerous observers, besides myself, have noted that it is best to wait 

 for a minimum of five days, usually a week or more, before bleeding 

 an animal, after the last injection it receives. The object of this is 

 to obtain the maximum amount of precipitin, by allowing a sufficient 



