consequent upon Inflammations of acute local Character. 163 



tions to the Thoma-Zeiss pipette are, the large surface relatively to cubic content, 

 the difficulty of drying the bead quickly enough for use in successive observations, 

 and the presumption that leucocytes will adhere to the bead. 



I have always counted both chromocytes and leucocytes in the same film of the 

 diluted blood, and in the same film enumerated the representatives of the various 

 kinds of leucocytes distinguishable, e.g., finely granular, coarsely granular, large 

 hyaline, small hyaline. I imagine the carrying out of the enumeration of all 

 the elements on one and the same film to be a point of importance. The methods 

 of counting in which the enumeration of chromocytes is carried out in one film, 

 that of leucocytes in a second, and the determination of the numerical proportion 

 between varieties of leucocytes in a third and fourth, let a number of possible and 

 probable variants into the observation which are excluded in carrying out the whole 

 operation upon one and the same large film. Certain countings it is naturally 

 impossible to combine in one and the same film ; for instance, those dependent on 

 the colour reactions introduced by Ehrlich cannot be combined with enumerations 

 on a living film ; but it is possible to translate the one results into the other, and to 

 make in that way the two modes of counting yield, as it were, control observa- 

 tions. 



for diluting the blood, I haye used the following solution : 

 Distilled water 300 grams. 

 Sodium chloride 1*2 

 Neutral potass, oxalate 1*2 

 Ehrlich's purified methyl blue . . O'l gram. 

 j.he chromocytes are not laked in it for several hours at the ordinary tempera- 

 ture of the room. The leucocytes of the dog, cat, and rabbit are not killed by 

 immersion in it for several hours ; they are reduced to a sluggish condition, and at 

 the ordinary temperature of the room do not locomote over the floor of the counter. 

 This fluid is preferable to Thoma's 0'3 per cent, acetic solution, which soon kills 

 the leucocytes outright, and rapidly destroys much of their finer structural charac- 

 ter. The object of the acid solution is to render invisible the chromocytes by 

 laking them. When blood is diluted only ten times, as is usual for counting leuco- 

 cytes in the Thoma-Zeiss apparatus, the number of chromocytes present tends to 

 obscure the leucocytes. Myself, I met that difficulty in my earlier countings 

 (although chromocytes and leucocytes were always, both of them, enumerated in 

 one and the same film), by rendering the chromocytes, after counting them, 

 invisible by freezing, and proceeding to count the leucocytes. The freezing waa 

 done by placing the counter on a carefully levelled freezing microtome, freezing the 

 film for a few seconds, and then letting it thaw again. Most of the chromocytes 

 are thus laked, and the leucocytes are most of them little altered. The difficulty 

 arising from condensation of moisture on the cover glass is met by using the water 

 immersion objective. It seems better, however, to dilute the blood more freely than 

 ten times, and not to freeze the film. I have latterly always used the solution in the 

 proportion of 49 parts to 1 part of blood. This admixture allows of the chromocytes 

 being easily counted, the normal blood of the dog offering then about 33 chromocytes 

 per square on the floor of the counter. 



In counting leucocytes one of the most serious mishaps that can occur is for 

 the leucocytes to cluster or " ball." It is obvious that where this has happened 

 the enumeration is useless. The hyaline leucocytes seem less sticky than do 

 the granular leucocytes. There is always, however, a tendency for all leuco- 

 cytes to clump in this way. In the above fluid in the above proportion, I have 

 had to reject very few observations on account of clumping. The basis obtained 

 for numerical calculation is, of course, reduced by increase of dilution. This 





