,l.\.l/'//17,.l.\7N O/.' M.LKItCY 193 



tlie uufoniHHl forcijiii pmrtcins to the difjestive complement, a view 

 in harmony with tlie prevailing tendeiiey to correlate tlie inunimity 

 reaction witli defense through enzj'niatic hydrol^'sis. 



Precii)itiii appeals in the blood generally about six days after in- 

 jection of the ])rotein, but disappears after injection of eacli subse- 

 quent dose of protein, to reappear again after a somewhat sliorter 

 lapse of time. After injections are stopped, the precipitin disap- 

 pears rather rapidly, but never appears in the urine, although it 

 may enter the fetal blood from the blood of pregnant female animals. 

 The presence of precipitins in the blood does not seem to prevent 

 the excretion of the foreign protein in the urine, nor are the animals 

 less susceptible to the toxic action of the foreign protein; indeed, the 

 reaction is even stronger in the immunized animals, and sometimes 

 the ordinary dose becomes fatal. Certain antibodies are carried down 

 with the precipitates formed when the serum containing them reacts 

 under proper conditions with an antiserum ; e. g., diphtheria antitoxin 

 is precipitated when added to the serum of a rabbit immunized to horse 

 serum. This is not true of all antibodies, however.^^ As the pre- 

 cipitates formed in the precipitin reaction, when injected into a guinea- 

 pig make it passively hypersensitive to the protein used as antigen in 

 the precipitin reaction, it would seem that the precipitin and the 

 anaphylactin are identical (Weil),^^ or at least closely associated. 



Chemical Properties. — In its chemical nature precipitin resembles 

 the "antibodies'' generally, being precipitated in the euglobulin 

 fraction of the serum/ and slowly destroj'ed by trypsin, rapidly by 

 pepsin. It cannot be separated from the serum proteins. The pre- 

 cipitation by precipitins is not an enzyme action, for the precipitins 

 are used up in the process. It apparently does not differ from pre- 

 cipitations of colloids by other colloids of opposite electrical charges, 

 except in that the reaction is specific. 



ANAPHYLAXIS OR ALLERGY 

 In many instances the injection of a foreign protein into an ani- 

 mal produces severe, perhaps fatal, intoxication. With some pro- 

 teins this natural toxicity is very marked, — thus eel serum is fatal 

 to rabbits and dog-s in doses of 0.1 to 0.3 c.e. per kilo, and foreign 

 sera are commonly toxic to other animals; e. g., fresh bovine and 

 human serum are quite toxic to" guinea-pigs. This so-called "pri- 

 mary" toxicity is reduced or destroyed in most cases by heating to 

 56° for 30 minutes.*^ Almost any non-toxic soluble protein, however, 

 may be made toxic for animals by giving the animal a small dose of 



3a See Gay and Stone. Jour. Immunol., 1916 (1), 83. 



3b Jour. Immunol., 191 6 (1), 1. 



*Fiuick (Cent. f. Bakt. ( Ref. ) . 100.5 (36). 744) states tliat if tlie precii)itin 

 serum is very strono:, part of the precipitin comes down in the pseudoiriobulin. 



4a The nature of the toxic agent is unknown, hut there is reason to helieve that 

 it is formed, at least in part, during- the coagulation of the drawn blood. 

 13 



