32 THE CIRCULATING LIQUIDS OF THE BODY 



in the serum of any other kind of animal. Thus, if human blood 

 or serum is repeatedly injected at short intervals into a rabbit, the 

 serum of the rabbit will cause a precipitate in diluted human blood 

 or serum, but not in the blood or serum of other animals, except 

 that of monkeys, where a slight reaction may be obtained. The 

 specific bodies which cause the precipitation are termed precipitins. 

 The phenomenon has been made the basis of a method of dis- 

 tinguishing human blood for forensic purposes. Other animal 

 fluids and solutions containing tissue proteins likewise give rise to 

 the production of precipitins. Thus, when cow's milk is injected 

 into a rabbit, the rabbit's serum acquires the power of precipitating 

 the caseinogen of cow's milk. Indeed, the response of the animal 

 body to the presence of foreign proteins is so catholic, and at the 

 same time so approximately specific, that many artificially isolated 

 proteins, even those of vegetable origin, after as careful purifica- 

 tion as possible, occasion, when injected, the production of anti- 

 bodies which will precipitate from a solution only the variety of 

 protein injected, or sometimes also, though in slighter degree, pro- 

 teins nearly related to it. 



Anaphylaxis. Under certain conditions the injection of a toxin, a 

 serum, or a protein solution, instead of eliciting an immunity reaction 

 which tends to combat the effects of a subsequent injection of the same 

 material, produces the opposite result namely, a sensitization of the 

 animal which renders the second dose far more harmful than the first. 

 Thus, Richet found that animals into which eel serum, or the poison 

 contained in the tentacles of Actinaria, was subcutaneously introduced 

 became much more sensitive to the toxic action of a second injection. 

 This phenomenon he designated anaphylaxis, as being the opposite of 

 the prophylaxis or protection afforded by previous treatment with the 

 toxins hitherto studied. Later on it was discovered that the sub- 

 cutaneous injection of a great variety of proteins alien to the animal 

 into which they are introduced causes anaphylaxis. Only very minute 

 amounts are necessary for the first or sensitizing dose, and an interval 

 considerably greater than that employed in the production of an 

 immune serum (p. 31) is allowed to elapse before the second injection 

 is made. The symptoms induced in the sensitized animal by a subse- 

 quent dose of the same material used in sensitization differ somewhat 

 in different animals, but may be designated in -general terms as those 

 of collapse or shock (anaphylactic shock). They have been especially 

 studied in the rabbit and guinea-pig, the heart being particularly affected 

 in the former, and the lungs in the latter. The symptoms are very 

 severe, and manifest themselves within a very short time (a few minutes) 

 of the injection. A large proportion of the animals die. If an animal 

 recovers, it does so suddenly, and for some time afterwards it is in- 

 sensitive to the particular protein. While the real nature of protein 

 sensitization or anaphylaxis is not as yet understood, it affords a new 

 and delicate test for the detection and discrimination of proteins, and 

 has already been utilized in a number of practical applications. For 

 instance, the sophistication of sausages with other than the orthodox 

 ingredients e.g., with horseflesh can be thus exposed, since an animal 

 sensitized by horseflesh will exhibit anaphylaxis to horseflesh, but not 

 to beef or pork. In like manner, the anaphylactic reaction may be 



