METHODS OF STUDYING H^MOLYSINS. 327 



to observe aseptic precautions; usually all that is required is to 

 collect the blood in dry sterile vessels, avoiding contamination with 

 dirt, etc. Hence the troublesome method of collecting blood from 

 the carotid of the animals will only then be undertaken if for some 

 reason asepsis is necessary or a large yield of blood is required. 

 In the latter case the yield of blood can be considerably increased 

 toward the end of exsanguination by rythmic compression of the 

 cardiac region. With goats, sheep, etc., the blood can easily be 

 obtained without any previous dissection by means of a suitable 

 canula thrust through the skin directly into the jugular vein which 

 has been distended by compression on the cardiac side. This is the 

 method commonly employed in obtaining the therapeutic sera from 

 horses. In this way small amounts of blood can be drawn from the 

 animals a great many times. Smaller animals, such as dogs, rabbits, 

 guinea-pigs, and rats, are most readily bled by anaesthetizing them, dis- 

 secting off the skin of the thigh and then with one stroke cutting both 

 the femoral artery and vein. From rabbits small amounts of blood 

 are easily obtained by incising the ear with a scissors or by means 

 of a hypodermic needle introduced into the marginal ear vein. Small 

 amounts of blood can be obtained from birds from the large wing 

 vein; in the case of geese and ducks the web of the foot can be incised. 

 For purposes of obtaining serum the blood is collected in cylindrical 

 vessels and allowed to coagulate spontaneously. It is kept hi the 

 refrigerator until the serum has separated. Several hours after 

 collecting the blood, it is well to loosen the clot from the sides of the 

 tube by means of a glass rod or spatula, for if this is not done the 

 serum may not separate. Small amounts of blood are best allowed 

 to clot in cylindrical glasses or tubes placed slantingly. After clotting 

 has occurred the vessel is placed upright. The serum which separates 

 will then flow to the bottom and can be poured off the next day. 

 If the serum is clouded with blood-cells, these are to be removed as 

 soon as possible. 1 



When the serum is poured off the first time the vessel containing 



1 An excellent centrifuge with a capacity up to 200 cc., but which can also 

 be had for larger quantities, is that made by Runne, the mechanic in Heidelberg 

 University. This machine is made either for water or electric power, and runs 

 exceedingly smoothly. For centrifuging smaller quantities of fluid, and espe- 

 cially for sedimenting blood-cells from dilute blood suspensions, the hand cen- 

 trifuge designed by Steenbeck-Litten, and made by F. and M. Lautenschlager 

 in Berlin, is excellent. 



