58 BIOLOGY OF THE PROTOZOA 



granules, but they rarely present the homogeneous appearance of a 

 spermatozoon nucleus, the individual granules, although closely 

 packed, being recognizable (Fig. 22). 



Certain constantly recurring substances are characteristic of 

 protozoan as of metazoan nuclei, but some types of arrangement and 

 com})ination of these substances are typical of Protozoa and are 

 rarely found in Metazoa. The most universal of these nuclear con- 

 stituents are (1) chromatin, Avhich is sometimes called nuclein or 

 identified as such; (2) linin, also called achromatin, nuclear retic- 

 ulum, achromatinic framework, etc., which is continuous with the 

 alveolar network of the cytoplasm; (3) nuclear membrane which is 

 composed of linin, and forms a permeable partition or wall between 

 cytoplasm and nucleoplasm; (4) nuclear sap or nuclear enchylema 

 filling the spaces of the linin reticulum; this seems to be identical 

 with the intra-ah'eolar substance of the c\toplasm; (5) plastin, often 

 so-called without being specifically identified as such; also termed 

 paranuclein, or pyrenin. Plastin in combination with chromatin 

 forms an intranuclear body, usually called the "karyosome," while 

 by itself plastin forms true nucleoli which are comparatively rare 

 in Prott)zoa. In addition to these a sixth constituent, kinetic 

 elements are characteristic of protozoan nuclei, and these in the 

 present work will be called endnbasal bodies. 



It must be frankly admitted that very little is known in regard 

 to the chemical nature of these various constituents of the nuclei 

 in Protozoa and much confusion exists in the literature owing to 

 the promiscuous use of these terms in relation to structural elements 

 of the nucleus without knowledge of the actual chemical make-up. 



(a) Chromatin.— Few investigations of a purely chemical nature 

 have been made on chromatin of Protozoa. The usual procedure 

 is to designate as chromatin all structures of the nucleus or cyto- 

 plasm which stain with the so-called nuclear dyes, or to interpret 

 chromatin mainly on a morphological basis. Microchemical tests 

 of all protoplasmic substances are made primarily on the basis of 

 solubility or insolubility with acids, alkalies, salts, etc., and the 

 microscopical picture presented after such treatment leads to the 

 conclusion that certain structures are made up of certain substances. 

 Such tests do not prove that a given structure is composed of a 

 definite substance and is not a mixture of substances, but they are 

 useful in the main to indicate that different structures are essentially 

 different in chemical make-up even though the exact chemical com- 

 position remains a secret. Kossel, Miescher and others have shown 

 that the chromatin bodies composed of the chemical substance 

 nuclein are not dissolved luider the action of artificial gastric juice 

 (pepsin and trypsin in appropriate acid and alkaline media) w^hile 

 other portions of the nucleus such as nucleoli, reticulum and plastin 

 are entirely dissolved. On the other hand chromatin bodies are 



