ANATOMICAL ELEMENTS. 13 



of mucous membranes, following irritation, and in inflammatory products, 

 when they are called pus-corpuscles. They are globular, with a smooth sur- 

 face, somewhat opaque from the presence of more or less granular matter, 

 white, and larger than the red corpuscles. In examining the circulation 

 under the microscope, the adhesive character of the leucocytes as compared 

 with the red corpuscles is readily noted. The latter circulate with great 

 rapidity in the centre of the vessels, while the leucocytes have a tendency to 

 adhere to the sides, moving along slowly, and occasionally remaining sta- 

 tionary for a time, until they are swept along by a change in the direction or 

 force of the current. 



The size of the leucocytes varies somewhat, even in any one fluid, such as 

 the blood. Their average diameter may be stated as 2 ^ 00 of an inch (10 /n). 

 It is in pus, where they exist in greatest abundance, that their microscopical 

 characters may be studied with most advantage. In this fluid, after it is 

 discharged, the corpuscles sometimes present remarkable changes in form. 

 They become polygonal in shape, and sometimes ovoid, occasionally present- 

 ing projections from their surface, which give them a stellate appearance. 

 These alterations, however, are only temporary ; and after twelve to twenty- 

 four hours, they resume their globular shape. On the addition of acetic acid 

 they swell up, become transparent, with a delicate outline, and present in 

 their interior one, two, three or even four rounded, nuclear bodies, generally 

 collected in a mass. This appearance is produced, though more slowly, by 

 the addition of water. In some corpuscles a nucleus may be seen without the 

 addition of any reagent. 



Leucocytes vary considerably in their external characters in different situ- 

 ations. Sometimes they are very pale and almost without granulations, 

 and sometimes they are filled with fatty granules and are not rendered clear 

 by acetic acid. As a rule, they increase in size and become granular when 

 confined in the tissues. In colostrum, where they are called colostrum-cor- 

 puscles, they generally undergo this change. As the result of inflammatory 

 action, when they are sometimes called inflammatory or exudation-corpuscles, 

 leucocytes frequently become much hypertrophied and are filled with fatty 

 granules. 



The deformation of the leucocytes to which allusion has already been 

 made is sometimes so rapid and changeable as to produce creeping move- 

 ments, due to the projection and retraction of portions of their substance. 

 These movements are of the kind called amoeboid and are supposed to be 

 important in the process of migration of the corpuscles. 



The relative number of leucocytes, can only be given approximately. It 

 has been estimated by counting under the microscope the red corpuscles and 

 leucocytes contained in a certain space. The average proportion in man is 

 probably 1 to 750 or 1000. It has been found by Hirt, whose observations 

 have been confirmed by others, that the relative quantity of leucocytes is 

 much increased during digestion. He found, in one individual, a proportion 

 of 1 to 1800 before breakfast ; an hour after breakfast, which was taken at 

 8 o'clock, 1 to 700 ; between 11 and 1 o'clock, 1 to 1500 ; after dining, at 1 

 3 



