268 PHYSIOLOGICAL CHEMISTRY. 



Blood Tests with Serum. The method of utilizing these generaliza- 

 tions is essentially this. Rabbits are the animals commonly used for ex- 

 periments, since they bear the treatment in general well and yield a fairly 

 large quantity of immunized blood later. Each rabbit is treated by injec- 

 tion with the blood serum of one animal, these injections being repeated 

 a number of times, through several weeks. Then the rabbit is killed, 

 bled and the blood allowed to stand for separation of clot. The clear 

 serum is preserved in sealed tubes for future use, sometimes with, some- 

 times without addition of an antiseptic, as putrefaction does not appear 

 to impair the reaction. By immunizing rabbits separately with the blood 

 of man, the ox, horse, pig, dog, sheep, goat, chicken, etc., a whole series 

 of test anti sera will be obtained, with which it is possible to identify 

 most of the common bloods. Not much blood is required in the tests. 

 A few drops of blood, from a dried clot for example, is soaked in water 

 or normal salt solution, the liquid obtained filtered to clarify it and treated 

 in a small test-tube with two or three drops of the test-serum. The liquid 

 to be tested need not be strong. In practice it should be divided into a 

 number of small portions in test-tubes and each portion should receive 

 a few drops of an immunized rabbit serum. Precipitation or clouding 

 will occur in the tube to which the corresponding anti serum is added. 

 For example, if the original clot of blood was human blood the extracted 

 dilute serum in all the tubes, except the one to which rabbit blood im- 

 munized with human blood was added, will remain clear; other tubes with 

 portions of the extracted clot show no reaction with the few drops of 

 rabbit sera immunized with the blood of other animals. 



The medico-legal importance of this reaction has already been recog- 

 nized and tested in many ways. The blood of certain monkeys seems 

 to react as does human blood, but those who have practiced the test most 

 testify as to its certainty and wide applicability in distinguishing between 

 human blood and the blood of the common domestic animals. 



The Cytotoxins. This name is given to certain anti com- 

 pounds in blood which are destructive of form elements. The 

 anti bodies before considered deal with soluble substances, but 

 here we have to consider something whose power extends to 

 the breaking down of cell structures, whether of the blood cor- 

 puscle or of bacteria. In the one case the term hemolysin is 

 used to describe the anti body ; in the other case the term bac- 

 teriolysin is employed. In their mode of action these agents 

 appear to be much alike and both are found in normal bloods. 

 Both also may be greatly increased artificially. 



The hemolytic action of one blood on another was first ob- 

 served in experiments on blood transfusion which have been 



