DIFFERENTIAL LEUCOCYTE COUNT 211 



reaction. To test for it make a film in the ordinary way, dry 

 and mount it without fixation in the following mixture : 



Iodine i part. 



Iodide of potassium 3 parts. 



Saturated watery solution of gum acacia 100 parts. 



This should not be used more than a fortnight after it has been 

 made. A simpler but equally good method is to expose the film 

 to the fumes of solid iodine for a few hours. This can be done by 

 fixing the film (without previous treatment of any sort) at the top 

 of a wide-mouthed bottle containing the substance ; it is then 

 mounted in oil or balsam. Allow it to act for a quarter of an 

 hour or more, then examine with a J^-inch lens in a white light 

 — daylight if possible. In cases where the reaction is present 

 a variable number of the polynuclears will be found to contain 

 granules or masses of a reddish-brown or mahogany colour ; 

 sometimes there are large masses, and sometimes almost the 

 whole of the protoplasm appears brown. 



The importance of this reaction is that it usually occurs, and 

 is indeed very marked, in the cases of severe sepsis in which 

 there is no increase of the total leucocyte count (see p. 198), as 

 well as in suppuration. It occurs in other conditions, such as 

 pneumonia, hooping-cough, uraemia, etc. In many cases a small 

 percentage only of the cells is affected, and a good search must 

 be made. 



The fact that it occurs in so many diseases detracts somewhat 

 from its value in diagnosis, but when the question is simply the 

 presence or absence of pus — e.g., in appendicitis — a positive result 

 will usually indicate that suppuration has occurred, and vice versa. 

 Hence it is sometimes of value when the leucocyte count yields 

 uncertain results — i.e., figures between 16,000 to 20,000 per cubic 

 millimetre. 



Myelocytes. — Ehrlich's myelocytes occur in small numbers in 

 many infectious diseases, especially diphtheria, and occasionally 

 in forms of anaemia, but they are only present in large numbers 

 in myeloid leucocythaemia. Cornil's myelocytes are practically 

 limited to the latter condition, where the two forms frequently 

 together make up 60 per cent, of all leucocytes. 



Eosinophiles. — An increase of eosinophiles (eosinophilia) occurs 

 to a small extent in numerous diseases, and is of diagnostic 

 importance in the following : 



I. In diseases due to animal parasites. Here the increase may 



