12 PROTISTS AND DISEASE 



acid (Chamberlain), also with chloro-iodide of zinc and iodine ; 

 and dissolving in saturated solution of copper hydrate. 



Where fungi are present one might expect these reagents 

 would reveal them by colouring their cellulose, but the re- 

 actions are of value only when positive. It is rare to find 

 fungi that respond. Fungal cellulose often requires long 

 maceration in 15 per cent, potash solution before it may 

 react. In Mycetozoa de Bary obtained the reaction but 

 once in the innermost layer of the sporangium wall of 

 Trichia varia, and had many negative results. The capillitia 

 of Didymium and Stemonitis changed to violet with the 

 acid alone. 



Woody fibre is composed chiefly of lignin, a modification 

 of cellulose, but does not react in the same way. In pro- 

 tozoa, chitin, a nitrogenous substance akin to keratin, takes 

 the place of cellulose, though one Rhizopod, Chlamydomyxa, 

 is partially enclosed in a capsule of cellulose. Cellulose also 

 forms the tunic of Ascidians, animals near the vertebrates 

 in organisation. 



Chromatin and Nuclei. The living nucleus can be 

 studied easily in many protists and cells. It contains 

 refracting material which stains readily ; hence called 

 chromatin (Flemming, 1879). When this is not diffused 

 through the whole nucleus we see in fixed preparations that 

 it lies in a net which is continuous as a rule with the cyto- 

 plasm through the nuclear membrane. This supporting 

 net is called linin, doublet of linen (Schwarz, 1887). 



