126 METHODS OF EXAMINING SERUM 



used, being smaller with several doses of the latter than with 

 a single dose ; in estimations of the dose of complement, it is 

 accordingly advisable to use the optimum amount of immune- 

 body, in the present instance about five hemolytic doses. The 

 activity of a serum as complement varies considerably, and 

 each sample must be separately tested. 1 The above will serve 

 as an indication of the fundamental methods ; for further 

 details, special papers on the subject must be consulted. 

 Corpuscles treated with sufficient immune-body to produce 

 complete lysis on the addition of complement are usually 

 spoken of as sensitised corpuscles. 



The Removal of Blood-Samples from Rabbits, etc.— In such work 

 as that just described, it is often convenient to watch the progress of an 

 immunisation procedure by removing a sample of blood without the 

 animal being killed. With proper care any amount of blood up to one- 

 third of that contained in the body can be removed from the ear vein of 

 a rabbit. The animal, which must not be flurried, is placed on a bench, 

 and its body kept warm by being covered with a cloth. The root of the 

 ear should be shaved over the marginal vein, the hairs on the edge of the 

 ear should also be clipped short. It is best to have the ear dry, Us the 

 evaporation of a fluid causes contraction of the vessels. In a great deal 

 of hemolytic work absolute sterility of the sample is not necessary, so 

 that washing the ear is not required. When sterile blood is desired, the 

 precautions detailed on p. 45 may be applied. A frosted incandescent 

 electric lamp, such as is used for microscopic illumination, is placed lighted 

 an inch or two from the ear. The left hand of the operator should cover 

 the animal's head in front of the ears, the thumb and index-finger being 

 left free to compress the vein at the foot of the ear. In this way not 

 only is the animal's eye protected from the glare of the lamp, bat the 

 distance of the latter from the ear can be regulated so as to keep it at 

 what to the operator's hand is a pleasant warmth. In a minute or two 

 the ear vessels will dilate, and the vein, being compressed at the root, a 

 lateral opening is made with a bayonet-pointed surgical needle (the 

 triangular-pointed needles supplied with the Gowers-Haldane hremo- 

 globinometer are also very suitable), and the blood allowed to drop into a 

 sterile test-tube. Usually waves of contraction of the ear vessels will be 

 observed to occur, the passing off of which must be waited for, and from 

 time to time the clot must be gently squeezed out of the opening in the 

 vein with the flat side of the needle, or it may be necessary slightly to 

 enlarge the opening. The blood should be allowed to clot completely, 

 and then, by means of a sterile platinum needle, the clot should be loosened 

 from the sides of the tube in order that it may freely contract. The tube 

 should be placed in the ice-chest till the following morning, when the 

 serum can be pipetted off with a sterile, nippled pipette. 



Daily samples can thus be obtained from an animal. If care be taken 



1 Complement rapidly (often within twenty-four hours) loses its strength 

 when kept at room temperature. It can, however, be preserved for a consider- 

 able time at or near its original strength if it be kept frozen. Even if this be 

 done, however, the strength of the complementary serum must be titredat 

 the commencement of every experiment in which it is employed. 



