Physical Chemistry and Yeterinahy Science. 187 



pected of suffering from enteric fever leads t(» the correct diagnosis of 

 the disease. 



The possibility of artificial immunisation has been used as quickly 

 as possible to cure and prevent animal and liuman diseases. There are 

 three methods : — 



(1) Passire inimittiitaifwu by the injection of antitoxic <ir iiiiero- 

 bicide serum which has been produced in another animal. The inmiunity 

 of the treated animal commences immediately after injection, but only 

 lasts for the short time the antibodies remain in the blood ; this method 

 is a curative one, and has proved very successful in humtin diphtheria. 



(2) Active immiuiixatioti, produced by injection of virus or vaccine. 

 The immunity only arises after a certain time, but usually remains for 

 a considerable time, in some cases for years. 



(3) The simnltan-method, being a combined injection of \irus and 

 serum. 



In South Africa the last two mentioned methods are used fur the 

 prevention of the following stock diseases : — 



(a) Rinderpest. An active immunisation by simultaneous injec- 

 tion (if virulent blood and anti-servim or by injection of bile (Koch). 



(6) Pleuro-pneumonici of cattle, by active immunisation produced 

 by fully virulent microbe culture. 



(c) Black Quarter Evil is prevented by actively immunising with 

 vaccine — that is to say, a virus attenuated by heat and dr3'ing. 



(d) Redwater. Active immunisation with virulent blood. 



(e) Blue tongue in sheep, by vaccination with virulent l)lood 

 (Theiler). 



( /■ ) Piroplasmosis or biliary fever in efjuines by vaccination with 

 attenuated virus (blood) (Theiler). 



i'j) Horse-sickness in mules is prevented by subcutaneous injection 

 of virulent blood simultaneously with immune serum (Theiler). 



The ethcacity of the innnune bodies in the respective anti-sera in 

 vivo having been evident, it was necessary to study the phenomena of 

 immunity quantitively, and experiments were made in the test tube as 

 -much as possible. After considerable discussion on the nature of the 

 formation of the compound antibody-antigen, physical chemistry has 

 recently furnished explanations. 



Antibodies are undoubtedly albuminoid substances ; as the other 

 albuminoids of the serum exist there only in the colloidal stage, it had 

 to be expected that tlie immune bodies are also colloidal. Indeed, 

 ample ca idence has been brought forward that it is so (Zangger). The 

 colloidal state of every substance is a great obstacle to chemical re- 

 action (Duclaux), hence it is quite natural that the reactions of the 

 immune substances ai-e — especially with regard to their tjuantitixe pro- 

 portions — colloid reactions, similar to absorptions, and their la^\■s must 

 therefore be of a physical or physical-chemical nature. 



The following are the direct proofs of the colloidal character of 

 the immune substances (Zangger). They are pseudo-solutions with no 

 defined critical points, optically inhomogeneous systems, tra\ersing 

 very slowly through membranes or not at all ; they have no electrical 



