264 SCIENCE PROGRESS 



In certain pathological states there may be an increase or 

 decrease, relative or absolute, of any or all of these varieties 

 of leucocyte, whilst the blood may also contain abnormal 

 forms of white cells constituting the various types of myelocyer 

 developed from the bone marrow. 



In the present communication it is with only two of these 

 varieties of leucocyte that I propose to deal, incorporating 

 therein some recent personal observations. These two varieties 

 are the polymorphonuclear neutrophilous leucocyte and the 

 large hyaline mononuclear leucocyte respectively. 



Polymorphonuclear Neutrophilous Leucocytes. — Of the various 

 types of leucocyte present in normal human blood, the poly- 

 morphonuclear neutrophilous leucocyte is the most abundant. 

 From 70 to 75 per cent, of all the leucocytes are of this variety. 

 In the various leucocytoses this number is greatly increased, 

 reaching 90 per cent, or upwards. It is an actively phagocytic 

 body, and on this account was termed " microphage " by 

 Metchnikoff. By the production of a ferment-like body 

 " microcytase," it digests and destroys bacteria and other 

 substances which have been phacocytosed. 



The most striking microscopic characteristic of this variety 

 of leucocyte is provided by the appearance of the nucleus 

 which, though always single, often appears to be multiple, on 

 account of the amount and character of the segmentation or 

 fragmentation which it presents. It is to this characteristic 

 that the designation polymorphonuclear, or as commonly 

 abbreviated polymorph, applied to these structures, is due. 



These nuclear segments vary greatly in number and may 

 present a great variety of shapes, being round, oval, looped, 

 S-shaped, Z-shaped, or quite irregular. 



In 1904 Arneth drew attention to the arrangement of the 

 nuclear segments of the polymorphonuclear leucocytes, and 

 pointed out that it was uniformly constant in normal blood, 

 and suggested that it should be employed as a basis for the 

 classification of these cells, and that a differential enumeration 

 of them could thus be made. Arneth made his classification 

 very elaborate, making use not only of the number, but also 

 of the shape, of the nuclear segments, together with their 

 arrangement. Without following Arneth into all the elabora- 

 tion and complexity of his classification, a sufficiently accurate 

 and comprehensive differential polymorphonuclear blood picture 

 may be obtained by classifying these cells according merely 

 to the number of the definite segments of the nucleus without 

 reference to their shape, size, or arrangement. This method 

 gives five classes as follows : Class I comprises cells with 

 unipartite or undivided nucleus ; Class II cells with bipartite 

 nucleus^ having two segments ; Class III with tripartite nucleus, 



