io8 



MANUAL OF BACTERIOLOGY. 



tion is concerned, in case samples of urine are to be sent by 

 mail; thymol should not be added if cultures are to be made. 

 Specimens of sputum, pus or blood may be collected con- 

 veniently in the form of thin smears upon cover-glasses. The 

 smears are fixed by passing through the flame three times. 

 Smears of blood are prepared as follows : Have two perfectly 

 clean, square cover-glasses. The finger, or the lobe of the ear, 

 having been carefully washed with water, alcohol and ether, is 

 punctured with a sterilized needle, and a small drop of blood 

 issues which is wiped away with a clean cloth. The second 

 drop of blood should be taken; it should be about the size of a 

 pin's head. No pressure should be exerted upon the skin. 

 This drop of blood is placed on one of the 

 cover-glasses. The other cover-glass is laid 

 upon the first, both being handled with for- 

 ceps. The drop of blood becomes flattened 

 out into a thin film. Immediately and be- 

 fore the blood has had time to coagulate 

 the two are slipped or slid away from each 

 other in a horizontal plane, not forcibly 

 pulled apart. In this way the blood will be 

 spread in thin films on the cover-glasses. 

 It is best to place the cover-glasses so that one does not cover 

 the other exactly, but so that the sides of the one lie diagonally 

 to the sides of the other, although their centers coincide (Fig. 

 37). Films of blood which are to be examined for the parasite 

 of malaria may be prepared in this manner. Drops of blood 

 to be used for the serum reaction for typhoid fever must be 

 large-sized. They may be collected on cover-glasses or pieces 

 of unsized paper and allowed to dry. In place of drops of 

 blood caught in this manner, the use of capillary tubes for 

 collecting the blood are to be preferred, since by this method 

 it is possible to obtain the serum free from corpuscles after the 

 clot forms in the tube. To test blood by culture methods 



Fig. 39. — Manner of 

 placing cover-glasses 

 in making films of 

 blood. — [After Cabot.) 



