542 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



a slide of blood, prepared in the following manner.* Take a clean 

 1x3 glass slide, and place near one end of it a drop of fresh blood 

 obtained from the prick of a needle in the finger, Tlien take another 

 slide with a ground edge, and place its edge into the drop of blood, 



inclining the second slide nntil it 

 Fm. 1-34. ^>s^ stands at an angle of about forty- 



five degrees towards tlie first one, 

 and draw it quickly but evenly 

 across the first slide (Fig. 134). 

 The result will be that tlic blood- 

 corpuscles are spread evenly upon 

 the slide, in one layer only, thus 

 giving an excellent view of their 

 outline. The blood-corpuscles 

 being lenticular bodies, with depressed centres, act like so many little 

 lenses of glass, and show diffraction rings if tlie light is not properly 

 arranged. It will, therefore, be seen that a slide prepared in this 

 manner forms one of the best, if not the best, tests for illumination, 

 as well as for flatness of fiehl." 



Tlje author then describes the arrangement of lamp, bull's-eye 

 condenser, concave mirror, and centering sub-stage condenser. 



" When properly illuminated, the blood-corpuscles should appear 

 as slightly olive-coloured disks, with a fine but intensely black out- 

 line, and on changing the focus there should appear a sjjot in the 

 centre. In order to fully appreciate the importance of each one of 

 the parts of the illuminating apparatus, and the necessity of having 

 them in their i)roper position, let the student first remove the bull's- 

 eye and let the light of the lamp alone fall upon the concave mirror, 

 without change in anything else. He will then see that the outline 

 of the blood-disks is much less sharply defined, and that there is a 

 suspicion of another outline within the outer one. Let him then 

 move the mirror bar slightly to the right or left of the median line, 

 and he will find that this second outline will be more marked and a 

 third one will be faintly seen, while the true margin of the corpuscle 

 is far from being sharj). Let him, finally, remove the substage con- 

 denser from its proj^er position, or throw it out of centre, or take it 

 off altogether, and he will find the blood-disks filled with rings and 

 with a bright spot in the centre." 



Microscopical Examination of Blood in the Diagnosis of 

 Disease. t — For the purpose of these investigations, M. Hayem re- 

 commends the use of a cell thus constructed : a thick jdane glass slide 

 has a disk made on it of about 4 mm. in diameter ; the rest of the slide 

 is silvered ; a small droj) of blood is placed on the disk and is covered 

 by a thin cover-glass, so that a layer of uniform thickness is obtained. 

 A little saliva placed round the edge will prevent any evajjoration. 



When blood is treated with a mixture of 200 grammes of distilled 

 water, one gramme of pure chloride of sodium, five grammes of sulphate 



* The author describes himself as being indebted to Dr. J. J. Wocdwurd for 

 this plan of making au even blood slide, 

 t Comptes Rendus, xcii. (1881) p. 89. 



