RECENT SCIENCE. 827 



microscopic constituents of the animal body.* Besides the cells 

 which constitute the animal tissues, there are in the body of man 

 and all vertebrates a number of free cells the white corpuscles 

 of blood and lymph and the wandering cells of the tissues which 

 exhibit all the characters of real amoeba?. Four different varie- 

 ties of these amoeboid cells, usually known under the general 

 name of leucocytes, have been described the distinctions between 

 them being chiefly based upon the shape and the numbers of their 

 nuclei ; but the commonest form is that of a speck of protoplasm 

 containing several nuclei which are connected by filaments of 

 nuclear substance, as well as a little radiated sphere which plays 

 such an important part in the bipartition of cells, f 



The leucocytes of both the higher and the lowest animals have 

 all the distinctive features of simple amoeba?. They protrude 

 pseudopodia, and move about like amoeba? (only the smaller ones, 

 usually described as lymphocytes, possessing this capacity to a 

 smaller extent), and, like amoeba?, they are endowed to a high de- 

 gree with the capacity of ingesting all kinds of small granules 

 which they find in their way, such as grains of coloring matter 

 suspended in water, and various smaller micro-organisms. It is 

 very easy to observe how leucocytes of the frog, the pigeon, the 

 guinea-pig, and so on, ingest bacilli by surrounding them with 

 their protoplasm ; and an immense literature, with illustrations 

 by photographs and correct drawings, has already been published 

 in order to show how various bacteria and micrococci are ingested 

 by leucocytes. In some cases the thus ingested bacilli are digested 

 that is, transformed into a soluble matter which is assimilated 

 by the protoplasm of the leucocyte, exactly in the same way as an 

 amoeba digests a diatom. In other cases the bacteria are for some 

 time kept alive within the leucocytes, and if the leucocytes have 

 been put into conditions which are unfavorable for themselves 

 but favorable for bacteria, the latter develop, and are set free. It 

 has also been seen pretty often that some bacilli propagate, by 

 means of spores, within the leucocytes, or that the spores which 

 have been kept for some time seemingly without life, begin to 

 develop and give origin to a new generation of bacilli. J 



* See his paper Immunity, in British Medical Journal, January 31, 1891. Also his last 

 most attractive and profusely illustrated work, Lecons sur la Pathologie comparee de l'ln- 

 flammation, Paris, 1802, which can be safely recommended to the general reader, notwith- 

 standing its rather technical title. Its subject is the struggle for life carried on within 

 organisms by the amoeboid cells against the microbes. 



f See Recent Science in the Nineteenth Century, May, 1892, p. 758. The best morpho- 

 logical description of leucocytes is to be found in Ehrlich's Farbenanalytische Untersuchung- 

 en zur Histologic und Klinik des Blutes, Berlin, 1891, quoted by Metchnikoff. 



\ P. Netschajeff, Ueber die Bedeutung der Leucocyten bei Infection der Organismen, in 

 Archiv fur pathologische Anatomie, 1891, Bd. exxv, p. 415. 



