VARIETIES OF LEUCOCYTES. 427 



zelle " can by a little searching be discovered. The exist- 

 ence of these various forms of young cell argues strongly 

 against pleomorphism explaining the existence of the 

 different adult forms. 



Two facts rise saliently out of the investigation of the 

 granulation contained in leucocytes. In the first place one 

 and the same individual cell never contains at one and the 

 same time two different kinds of granules : all the granules 

 within it are of similar quality, as least as far as they 

 can be tested by the microscopical reactions at present 

 available. If the cell at one time produced one kind of 

 granule, and at another time another, this is hardly what 

 would have been expected. In the second place the 

 granular material present in them is of extremely wide 

 distribution in the animal kingdom. For instance, the 

 eosinophil granule can be studied alike in the Vermes (24), 

 Mollusca (25) and Arthropods, as well as throughout all 

 classes of the Vertebrata. It would seem of very ancient 

 origin in the evolution of animal structure, and it must 

 possess physiological significance of some fundamental 

 kind. What that significance may be we have at present 

 very little opportunity of gauging ; it has been suggested 

 above that it may have to do with the formation of 

 haemoglobin, but the eosinophil substance is present in 

 some animals that are not possessed of any haemoglobin. 

 It has been mentioned above that this granule has some 

 bactericidal power (2), but inasmuch as that power can only 

 be exercised under abnormal conditions it is not to be con- 

 sidered an attribute which explains the normal production 

 of the material. 



An inquiry may be raised as to how far it is permissible 

 to consider cells to be necessarily of the same kind or closely 

 genetically connected simply because they contain granules 

 of the same material. If, for instance, the occurrence of 

 fat in cells be used for argument, in the same way it may 

 be urged that certain liver cells and certain connective 

 tissue corpuscles are closely allied structures. Certainly 

 some connective tissue corpuscles contain coarse oxyphil 

 granules of appearance and quality similar to those in the 



