944 KECORD OF CURRENT RESEARCHES RELATING TO 



preparations made on these principles, oven at an increased cost, when 

 they are really instructive, and it cannot be doubted when we see the 

 most common specimens of Pediculiis pubis sold in America for 

 5 fr. 75 c, in which country it is not rarer than it is in France." 



Counting of Blood-corpuscles.* — Professor Abbe has recently 

 published a paper on this subject, in which he refers in the first place 

 to an apparatus, the plan of which was suggested by Mr. E. Thoma, 

 of Heidelberg. It presents no special novelty in design, its value con- 

 sisting rathci" in the appropriate adaptation of the best means known, 

 and the careful technical construction by which the faults of the 

 measuring apparatus are kept within narrow limits, so that they may 

 be neglected in practice. 



The leading features are — (1) the method of mixing the blood so 

 as to dilute it in a simple known proportion, and (2) the special 

 apparatus for counting which enables the microscopist to take a 

 determinate volume of the diluted blood fluid. For the first Ma- 

 lassez's mixer is used, modified so as to facilitate the purifying and to 

 keep the consistency constant. The caj)illary tube holds about 6 

 mgr. of blood ; its volume, which is taken as unity, is made the one- 

 hundredth part of the volume of the mixing bulb (exact to about 0'5 

 per cent.). The correct length of the capillary is determined from 

 data as to the capacity of the tube and mixing bulb, obtained by 

 weighing, water being used for the latter instead of quicksilver, as on 

 account of the glass ball used for mixing, a non-adhering fluid would 

 not properly fill out the space. 



For counting, an adaptation is made of Hay em's chamber, which 

 consists of a slide to which a thin glass plate with a circular hole 

 is firmly cemented aud ground down parallel to the surface of the 

 slide, so that a superposed flat plate would enclose a stratum exactly 

 0*1 mm. deep. For cutting off a definite volume of this stratum, 

 instead of a micrometer in the eye-piece of the Microscope, Gower's 

 method is adopted, and divisions are cut on the bottom of the cham- 

 ber, so that a square millimetre is divided into small squares, the 

 sides of which are • 05 mm., and the area ^ J ^y square mm. As the 

 blood-corpuscles in the artificial serum of Malassez sink to the 

 bottom in a few moments, the contents of a thousandth of a cubic 

 millimetre in the field of the Microscope may be readily counted, 

 being the contents of any four of the divisions. When normal blood 

 is diluted in the proportion of 1 : 100, about fifty blood-corpuscles aro 

 found in this space, and the number being multiplied by 100, gives 

 the contents of the thinned blood per thousandth cubic millimetre, 

 which furnishes figures convenient for comparison. 



The divisions on the bottom of the counting apparatus are a great 

 advantage over the eye-piece micrometer, as they avoid the necessity 

 of ascertiiiuiug the value of the divisions of the latter, which of course 

 varies with the objective and Icngtli of the tube ; a fruitful source of 

 errors is avoided, and complete freedom is obtained in tho choice of 

 objectives aud magnifying power. 



* ' SB. Jen. Gesell. Med. uml Nat.' (1878). 



