APPENDIX 485 



This acts as a miniature gas-holder if fermentation of the medium 

 occurs. The tubes are finally steamed for twenty minutes for each of 

 three successive days. For the examination of water 1 c.c. is added to 

 each tube, and several are inoculated and incubated at 42 C. for forty- 

 eight hours. If the colon bacillus be present, the medium becomes 

 uniformly red, and is permeated with small gas bubbles, while the little 

 tube is filled with gas. Subsequently, plates may be made from the 

 tubes with .the bile-salt agar medium. 



Examination of Malarial Blood 



1. Fresh Blood. Thoroughly clean a cover-glass and wash a finger of 

 the patient. Then prick the finger and squeeze out a drop of blood. 

 This first drop of blood should be rejected. But when a second smaller 

 drop appears, just touch its surface with the clean cover-glass. Now 

 place the cover-glass on a clean slide, but do not exert any pressure 

 upon it. Under the weight of the cover-glass the blood will now spread 

 out into a very thin film. On examination under the microscope or by 

 the naked eye it will be seen that the blood corpuscles have, roughly 

 speaking, assumed the following zones : 



(a) A zone of scattered corpuscles immediately surrounding a central 

 portion empty of corpuscles and devoid of colour. This "scattered" 

 zone is composed of isolated, compressed, and much expanded 

 corpuscles. 



(6) Outside this first zone is one composed of corpuscles just touching 

 each other by the margin. This has, therefore, been called the single 

 layer zone. 



(c) The third zone lies still further outside, and is composed of 

 heaped-up corpuscles, overlapping each "other and often in rouleaux. 

 Beyond them is the area of free haemoglobin, and valuable as enabling 

 the observer to see if there are pigment parasites present in the blood. 



The ordinary pigmented amoeboid forms of the parasite will generally 

 be found in the single layer zone, whilst the flagellated bodies, if present, 

 will be seen chiefly in zone (c). 



Pigmented leucocytes may appear anywhere in the field of the 

 microscope. 



The intra-corpuscular parasites may generally be detected because 

 of their amoeboid movements, pigmentation, feeble definition, and effect 

 upon the corpuscle containing them. 



2. Stained Preparation. Whilst it is always best to examine malarial 

 blood in a fresh state if possible, it is generally desirable to make more 

 permanent preparations. This may be done as follows : Make upon a 

 clean slide a very thin film of the malarial blood (by drawing a needle 

 or edge of cigarette paper over film). Allow it to dry in the air. Then 

 wash the slide containing the dried film with weak acetic acid (say two 

 or three drops of glacial acetic to an ounce of water) to clear the 

 haemoglobin. This may also be accomplished by dropping on the slide 

 a little alcohol, which may be dried up in several minutes' time with 



