38o POPULAR SCIENCE MONTHLY. 



An exception to these two fundamental rules is found in tlie 

 single case of the leucocytes or white globules of the blood. They 

 have no fixed or determined place in the organism. Besides being 

 carried passively by the flow of the blood in a perpetual circula- 

 tion along with the red corpuscles, they possess a motion of their 

 own. They can swim in the current that carries them, fi:s them- 

 selves to the walls, and travel in a sort of creeping way, which has 

 been called the amoeboid motion. 



They are also exceptions to the second law, according to which 

 living cells can dispose only of liquefied matters. All solid bodies 

 that pass within reach of the leucocytes are seized and incorporated 

 by them, provided they are sm.all or inert enough to be enveloped. 

 The nature of the body is of little import. Whatever it may be, 

 it is swallowed and quickly inclosed within the mass of the leuco- 

 cyte and submitted to the dissolving action of its juices — or, in a 

 way, eaten. Hence the names " phagocyte," or devouring cell, given 

 to the enveloping white globule, and " phagocytosis " to the process. 

 No other element of the organism, or hardly any other, possesses 

 this singular faculty of seizure and swallowing (inglohemeni). 



All the other characteristics of the white globules flow from 

 these two of mobility and phagocytism, the significance of which 

 has been set in a clear light by M. Metchnikoff. These character- 

 istics are the attributes of the most primitive types of animal life. 

 They appertain to cells not yet differentiated, to the unicellular 

 organisms which occupy the first stages of life. They translate 

 the vital energy of elements still independent and isolated, with- 

 out definite place in the social organization and as yet without spe- 

 cial high function, but for that very reason better adapted to the 

 needs of the simplest animality. Their voracity is useful for the 

 preservation of the social organism. By eliminating old, ex- 

 hausted, diseased cells they rejuvenate the structure and prepare 

 the way for new generations. And when the fecundity of these is 

 exhausted the leucocytes come in to occupy the vacated situations, 

 and conduct the organism thus patched up through a senile degen- 

 eracy to natural death. 



The leucocytes, white globules, or phagocytes, by virtue of their 

 mobility, are found everj'Avhere — in the blood, in all the organs, 

 and in all parts of the body — but are perhaps most abundant in 

 the blood. The study of them proceeds slowly, and we are still 

 engaged in distinguishing the varieties among them. The most 

 abundant and best known of them — those which answer most closely 

 the description we have given — are those called the polynuclear, 

 neutrophilous leucocytes. They are colored with neutral hues, 

 and have a nucleus like a rolled-up scroll in structure. Other 



